Debug your models efficiently¶
This tutorial gives insights on how you can debug tespy models. The user interface of the current implementation might still need some refinement, so you are invited to raise issues in the github repository. We will change it based on the feedback. The outputs shown here are based on the following version of tespy:
from tespy import __version__
__version__
"0.11.3 - Rankine's Renaissance"
Simple model debugging¶
This tutorial will show a couple of things
How to extract the variables of the problem
before presolving step
after presolving step and identify the presolved variables
How to extract the applied equations of the problem
before presolving step
after presolving step and identify the presolved equations
How to read and fix the errors that are raised during presolving
How to debug structural errors and non-convergence with the structural analysis, the incidence matrix and the residuals
Model overview¶
The model we implement is a very simple heat pump model, just as implemented in the introductory Heat Pump tutorial.
Model code¶
from tespy.components import CycleCloser, SimpleHeatExchanger, Compressor, Valve, Motor, PowerSource
from tespy.connections import Connection, PowerConnection
from tespy.networks import Network
nw = Network()
nw.units.set_defaults(
temperature="°C",
pressure="bar",
pressure_difference="bar",
power="kW",
heat="kW",
enthalpy="kJ/kg"
)
grid = PowerSource("grid")
motor = Motor("motor")
cc = CycleCloser("cycle closer")
valve = Valve("valve")
evaporator = SimpleHeatExchanger("evaporator")
compressor = Compressor("compressor")
condenser = SimpleHeatExchanger("condenser")
c1 = Connection(cc, "out1", evaporator, "in1", label="c1")
c2 = Connection(evaporator, "out1", compressor, "in1", label="c2")
c3 = Connection(compressor, "out1", condenser, "in1", label="c3")
c4 = Connection(condenser, "out1", valve, "in1", label="c4")
c0 = Connection(valve, "out1", cc, "in1", label="c0")
nw.add_conns(c1, c2, c3, c4, c0)
e1 = PowerConnection(grid, "power", motor, "power_in", label="e1")
e2 = PowerConnection(motor, "power_out", compressor, "power", label="e2")
nw.add_conns(e1, e2)
Debug the model¶
Variable and equation identification¶
With nothing specified and trying to solve we will get an information, that the network is lacking fluid information.
nw.solve("design", init_only=True)
---------------------------------------------------------------------------
TESPyNetworkError Traceback (most recent call last)
Cell In[5], line 1
----> 1 nw.solve("design", init_only=True)
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2596, in Network.solve(self, mode, init_path, design_path, max_iter, min_iter, init_only, init_previous, use_cuda, print_results, robust_relax, skip_postprocess, oscillation_damping, block_solve, pause_on_block_failure, line_search)
2491 def solve(self, mode, init_path=None, design_path=None,
2492 max_iter=50, min_iter=2, init_only=False, init_previous=True,
2493 use_cuda=False, print_results=True, robust_relax=False, skip_postprocess=False,
2494 oscillation_damping=False, block_solve=True,
2495 pause_on_block_failure=False, line_search="stagnation"):
2496 r"""
2497 Solve the network.
2498
(...) 2594 documentation at tespy.readthedocs.io in the section "TESPy modules".
2595 """
-> 2596 self.presolve(
2597 mode, init_path=init_path, design_path=design_path,
2598 init_previous=init_previous, check=not init_only
2599 )
2601 if init_only:
2602 return
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2690, in Network.presolve(self, mode, init_path, design_path, init_previous, check)
2683 msg = (
2684 "Network information:\n"
2685 f" - Number of components: {len(self.comps)}\n"
2686 f" - Number of connections: {len(self.conns)}\n"
2687 )
2688 logger.debug(msg)
-> 2690 self._prepare_problem()
2691 self._presolve_pending = True
2693 if not check:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1039, in Network._prepare_problem(self)
1036 self._create_fluid_wrapper_branches()
1037 break
-> 1039 self._propagate_fluid_wrappers()
1040 # the fluid composition may have changed, the frames are rebuilt
1041 # lazily on access of the results
1042 for conn_type in self.conns["conn_type"].unique():
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1126, in Network._propagate_fluid_wrappers(self)
1120 if num_potential_fluids == 0:
1121 msg = (
1122 "The following connections of your network are missing any "
1123 "kind of fluid composition information:"
1124 f"{', '.join([c.label for c in all_connections])}."
1125 )
-> 1126 raise hlp.TESPyNetworkError(msg)
1128 for c in all_connections:
1129 c.mixing_rule = mixing_rule
TESPyNetworkError: The following connections of your network are missing any kind of fluid composition information:c1, c2, c3, c4, c0.
Then let’s specify the fluid and preprocess the network again. The check,
whether the number of specified parameters matches the number of variables of
the problem, runs automatically at the start of every solve. When running with
init_only=True the check is skipped and no error is raised, so we can use
that starting point in an interactive python environment to get started with
debugging.
c1.set_attr(fluid={"R290": 1})
nw.solve("design", init_only=True)
Now we can check the following information:
Which are the original variables of our model
Which of those variables have already been determined by the presolving
Which ones are the actual variables, that the model has to solve and which original variables of the model these variables represent
The original variables:
nw.print_variables_before_presolve()
Variables before presolving (22 total):
Object Property
-------- ----------
c0 m
c0 p
c0 h
c0 fluid
c1 m
c1 p
c1 h
c1 fluid
c2 m
c2 p
c2 h
c2 fluid
c3 m
c3 p
c3 h
c3 fluid
c4 m
c4 p
c4 h
c4 fluid
e1 E
e2 E
The variables solved already by the presolving step:
nw.print_presolved_variables()
Presolved variables (5 total):
Object Property
-------- ----------
c0 fluid
c1 fluid
c2 fluid
c3 fluid
c4 fluid
The actual variables of the problem: each has a number and a property type
(mass flow, pressure, enthalpy, fluid, …) and represents one or more of the
original variables. The represents column lists those with the label of the
connection they originate from.
nw.print_variables()
Variables after presolving (10 total):
# Property Represents
--- ---------- --------------------------------------
0 p c2 (p)
1 h c2 (h)
2 p c3 (p)
3 h c3 (h)
4 p c4 (p)
5 E e1 (E)
6 E e2 (E)
7 m c2 (m), c3 (m), c1 (m), c4 (m), c0 (m)
8 p c0 (p), c1 (p)
9 h c0 (h), c1 (h), c4 (h)
We can also check which equations of the model have been presolved in order to
retrieve the dependencies between the variables. E.g. the mass flow variable
just before represents all the mass flows in this model. We can see, that the
mass_flow_constraints have been solved for all components. The equations
indicated here can be inspected in the tables of the documentation on the
components and
connections.
nw.print_presolved_equations()
Presolved equations (11 total):
Object Equation
------------ ----------------------------
compressor mass_flow_constraints
compressor fluid_constraints
condenser mass_flow_constraints
condenser fluid_constraints
cycle closer pressure_equality_constraint
cycle closer enthalpy_equality_constraint
evaporator mass_flow_constraints
evaporator fluid_constraints
valve mass_flow_constraints
valve fluid_constraints
valve enthalpy_constraints
There is not yet an easy way to identify which variable was presolved by which. Next to the presolved equations we can also inspect, which equations are present in the actual model that needs to be solved iteratively.
nw.print_equations()
Equations after presolving (1 total):
Eq# Object Equation
----- ---------- ------------------------
0 compressor energy_connector_balance
With the equations we can also extract the variables these depend on.
nw.print_equations_with_dependents()
Equations with dependent variables (1 total):
Eq# Object Equation Dependent variables
----- ---------- ------------------------ ---------------------
0 compressor energy_connector_balance h1, h3, E6, m7
Impose parameters and check again¶
Now let’s impose a couple of boundary conditions:
No pressure drop in heat exchanges
Compressor efficiency
Motor efficiency
condenser.set_attr(dp=0)
evaporator.set_attr(dp=0)
compressor.set_attr(eta_s=0.8)
motor.set_attr(eta=0.97)
nw.solve("design", init_only=True)
Again, we can inspect, which variables have been presolved now. It does not change, because we did not impose any boundary conditions, where any of the variables can be directly determined from.
nw.print_presolved_variables()
Presolved variables (5 total):
Object Property
-------- ----------
c0 fluid
c1 fluid
c2 fluid
c3 fluid
c4 fluid
But if we check the actual variables of the system, we see that the number has been reduced. The two energy flows are now mapped to a single variable, and the pressure values before and after the heat exchangers have been also mapped to a single variable respectively.
nw.print_variables()
Variables after presolving (7 total):
# Property Represents
--- ---------- --------------------------------------
0 h c2 (h)
1 h c3 (h)
2 m c2 (m), c3 (m), c1 (m), c4 (m), c0 (m)
3 p c3 (p), c4 (p)
4 p c0 (p), c1 (p), c2 (p)
5 h c0 (h), c1 (h), c4 (h)
6 E e1 (E), e2 (E)
The reason for that can be seen in the presolved equations, where now we have three additional entries.
nw.print_presolved_equations()
Presolved equations (14 total):
Object Equation
------------ ----------------------------
compressor mass_flow_constraints
compressor fluid_constraints
condenser mass_flow_constraints
condenser fluid_constraints
condenser dp
cycle closer pressure_equality_constraint
cycle closer enthalpy_equality_constraint
evaporator mass_flow_constraints
evaporator fluid_constraints
evaporator dp
motor eta
valve mass_flow_constraints
valve fluid_constraints
valve enthalpy_constraints
And we also get one more equation in our model equations, that needs to be solved numerically: the compressor efficiency.
nw.print_equations_with_dependents()
Equations with dependent variables (2 total):
Eq# Object Equation Dependent variables
----- ---------- ------------------------ ---------------------
0 compressor energy_connector_balance h0, h1, m2, E6
1 compressor eta_s h0, h1, p3, p4
Or in a matrix view:
nw.print_incidence_matrix()
Incidence matrix:
h0 h1 m2 p3 p4 E6
----------------------------------- ---- ---- ---- ---- ---- ----
compressor.energy_connector_balance x x x - - x
compressor.eta_s x x - x x -
Let’s add more boundary conditions, because we are still missing a couple:
evaporation temperature level and superheating
c2.set_attr(T_dew=10, td_dew=10)
nw.solve("design", init_only=True)
Now we can see that the number of variables has been reduced by two. The reason for this is, that the presolver was able to identify pressure and enthalpy at the compressor inlet with the given boundary conditions.
nw.print_variables()
Variables after presolving (5 total):
# Property Represents
--- ---------- --------------------------------------
0 h c3 (h)
1 m c2 (m), c3 (m), c1 (m), c4 (m), c0 (m)
2 p c3 (p), c4 (p)
3 h c0 (h), c1 (h), c4 (h)
4 E e1 (E), e2 (E)
Since these two variables have now been presolved, the equation of the compressor has less dependents, as it is not necessary to solve for the respective variables anymore.
nw.print_equations_with_dependents()
Equations with dependent variables (2 total):
Eq# Object Equation Dependent variables
----- ---------- ------------------------ ---------------------
0 compressor energy_connector_balance h0, m1, E4
1 compressor eta_s h0, p2
We are still missing 3 equations as we have 5 variables in the problem and only 2 equations at the moment, so let’s add the missing specifications:
electrical power input
condensing temperature level and subcooling
c4.set_attr(T_bubble=60, td_bubble=0)
e1.set_attr(E=100) # 100 kW
nw.solve("design")
block 0 | scalar | iterations: 2 | residual: 0.00e+00 | compressor.eta_s
block 1 | scalar | iterations: 2 | residual: 2.15e-15 | compressor.energy_connector_balance
The solver output shows that the two remaining equations were solved as individual blocks in sequence. The block decomposition can be inspected directly, see the decomposition section for the background:
nw.print_blocks()
Block lower triangular decomposition (2 blocks):
# Kind Needs Equations Variables
--- ------ ------- ----------------------------------- -----------
0 scalar compressor.eta_s h0
1 scalar 0 compressor.energy_connector_balance m1
nw.print_incidence_matrix(block_order=True)
Incidence matrix:
Block h0 m1
------- ----------------------------------- ---- ----
0 compressor.eta_s X -
1 compressor.energy_connector_balance x X
Handle errors during presolving¶
Some errors can occur during presolving, for example:
You specify a linear change of specific variable while specifying both values simultaneously. In this case, the error message directly tells you which variables are linear dependent and that you specified more than a single value in that set (points to the labels of the connections/components).
e2.set_attr(E=97)
nw.solve("design")
---------------------------------------------------------------------------
TESPyNetworkError Traceback (most recent call last)
Cell In[26], line 2
1 e2.set_attr(E=97)
----> 2 nw.solve("design")
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2596, in Network.solve(self, mode, init_path, design_path, max_iter, min_iter, init_only, init_previous, use_cuda, print_results, robust_relax, skip_postprocess, oscillation_damping, block_solve, pause_on_block_failure, line_search)
2491 def solve(self, mode, init_path=None, design_path=None,
2492 max_iter=50, min_iter=2, init_only=False, init_previous=True,
2493 use_cuda=False, print_results=True, robust_relax=False, skip_postprocess=False,
2494 oscillation_damping=False, block_solve=True,
2495 pause_on_block_failure=False, line_search="stagnation"):
2496 r"""
2497 Solve the network.
2498
(...) 2594 documentation at tespy.readthedocs.io in the section "TESPy modules".
2595 """
-> 2596 self.presolve(
2597 mode, init_path=init_path, design_path=design_path,
2598 init_previous=init_previous, check=not init_only
2599 )
2601 if init_only:
2602 return
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2690, in Network.presolve(self, mode, init_path, design_path, init_previous, check)
2683 msg = (
2684 "Network information:\n"
2685 f" - Number of components: {len(self.comps)}\n"
2686 f" - Number of connections: {len(self.conns)}\n"
2687 )
2688 logger.debug(msg)
-> 2690 self._prepare_problem()
2691 self._presolve_pending = True
2693 if not check:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1050, in Network._prepare_problem(self)
1046 # this method will distribute units and set SI values from given values
1047 # and units
1048 self._transform_user_input_to_SI()
-> 1050 self._problem.build()
1052 # generic fluid property initialisation
1053 self._set_starting_values()
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:199, in Problem.build(self)
192 msg = (
193 f"Original problem: {self.num_original_variables} variables and "
194 f"{self.num_original_equations} equations, of which {num_affine} "
195 "equations were consumed by the affine variable elimination."
196 )
197 logger.debug(msg)
--> 199 self._presolve()
201 # counted only now: during the structure matrix assembly the
202 # specification and variable flags of the containers are transient,
203 # e.g. propagated fluid compositions read as set while their
204 # variable fractions are only marked during the presolving
205 self.num_specified_variables = 0
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:509, in Problem._presolve(self)
505 self._presolve_fluid_vectors()
507 # impose the user specifications on the affine groups first, so the
508 # first round of connection presolving already sees them as known
--> 509 self._presolve_linear_dependents()
511 # only scalar references are tracked: the fluid vectors were
512 # fully resolved above and their is_var holds a set of fraction
513 # names, not a boolean
514 known_references = set()
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:739, in Problem._presolve_linear_dependents(self)
733 var_str = ", ".join(variables_properties)
734 msg = (
735 "You specified more than one variable within a set of "
736 "linearly dependent variables.\n"
737 f" Variables: {var_str}"
738 )
--> 739 raise hlp.TESPyNetworkError(msg)
740 elif number_specifications == 1:
741 reference_data = self._variable_lookup[reference]
TESPyNetworkError: You specified more than one variable within a set of linearly dependent variables.
Variables: e1 (E), e2 (E)
We can see the same problem if we were to specify compressor pressure ratio: The compressor inlet pressure is determined from the compressor inlet state, the condenser outlet pressure is determined from the condenser outlet state and the condenser pressure drop is specified. By that also the compressor outlet pressure is known and you cannot specify the outlet pressure.
e2.set_attr(E=None)
compressor.set_attr(pr=4)
nw.solve("design", init_only=True)
---------------------------------------------------------------------------
TESPyNetworkError Traceback (most recent call last)
Cell In[27], line 3
1 e2.set_attr(E=None)
2 compressor.set_attr(pr=4)
----> 3 nw.solve("design", init_only=True)
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2596, in Network.solve(self, mode, init_path, design_path, max_iter, min_iter, init_only, init_previous, use_cuda, print_results, robust_relax, skip_postprocess, oscillation_damping, block_solve, pause_on_block_failure, line_search)
2491 def solve(self, mode, init_path=None, design_path=None,
2492 max_iter=50, min_iter=2, init_only=False, init_previous=True,
2493 use_cuda=False, print_results=True, robust_relax=False, skip_postprocess=False,
2494 oscillation_damping=False, block_solve=True,
2495 pause_on_block_failure=False, line_search="stagnation"):
2496 r"""
2497 Solve the network.
2498
(...) 2594 documentation at tespy.readthedocs.io in the section "TESPy modules".
2595 """
-> 2596 self.presolve(
2597 mode, init_path=init_path, design_path=design_path,
2598 init_previous=init_previous, check=not init_only
2599 )
2601 if init_only:
2602 return
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2690, in Network.presolve(self, mode, init_path, design_path, init_previous, check)
2683 msg = (
2684 "Network information:\n"
2685 f" - Number of components: {len(self.comps)}\n"
2686 f" - Number of connections: {len(self.conns)}\n"
2687 )
2688 logger.debug(msg)
-> 2690 self._prepare_problem()
2691 self._presolve_pending = True
2693 if not check:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1050, in Network._prepare_problem(self)
1046 # this method will distribute units and set SI values from given values
1047 # and units
1048 self._transform_user_input_to_SI()
-> 1050 self._problem.build()
1052 # generic fluid property initialisation
1053 self._set_starting_values()
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:199, in Problem.build(self)
192 msg = (
193 f"Original problem: {self.num_original_variables} variables and "
194 f"{self.num_original_equations} equations, of which {num_affine} "
195 "equations were consumed by the affine variable elimination."
196 )
197 logger.debug(msg)
--> 199 self._presolve()
201 # counted only now: during the structure matrix assembly the
202 # specification and variable flags of the containers are transient,
203 # e.g. propagated fluid compositions read as set while their
204 # variable fractions are only marked during the presolving
205 self.num_specified_variables = 0
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:546, in Problem._presolve(self)
537 for determination in c._presolve_determinations:
538 self._presolve_log.append({
539 "round": rounds,
540 "kind": "combination",
(...) 544 "requires": determination["requires"],
545 })
--> 546 self._presolve_linear_dependents()
548 newly_known = []
549 for linear_dependents in self._variable_dependencies:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:739, in Problem._presolve_linear_dependents(self)
733 var_str = ", ".join(variables_properties)
734 msg = (
735 "You specified more than one variable within a set of "
736 "linearly dependent variables.\n"
737 f" Variables: {var_str}"
738 )
--> 739 raise hlp.TESPyNetworkError(msg)
740 elif number_specifications == 1:
741 reference_data = self._variable_lookup[reference]
TESPyNetworkError: You specified more than one variable within a set of linearly dependent variables.
Variables: c2 (p), c3 (p), c1 (p), c0 (p), c4 (p)
You can also think of creating a circular dependency. For example, if you specify a relationship of mass flow in front and behind the cycle closer (or if you were to remove the cycle closer). Then the mass flow would form a circular dependency. As output of the error message you get the variables which are part of the circular dependency and the equations responsible for that.
compressor.set_attr(pr=None)
from tespy.connections import Ref
c1.set_attr(m=Ref(c0, 1, 0))
nw.solve("design", init_only=True)
---------------------------------------------------------------------------
TESPyNetworkError Traceback (most recent call last)
Cell In[28], line 7
3
4 from tespy.connections import Ref
5
6 c1.set_attr(m=Ref(c0, 1, 0))
----> 7 nw.solve("design", init_only=True)
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2596, in Network.solve(self, mode, init_path, design_path, max_iter, min_iter, init_only, init_previous, use_cuda, print_results, robust_relax, skip_postprocess, oscillation_damping, block_solve, pause_on_block_failure, line_search)
2491 def solve(self, mode, init_path=None, design_path=None,
2492 max_iter=50, min_iter=2, init_only=False, init_previous=True,
2493 use_cuda=False, print_results=True, robust_relax=False, skip_postprocess=False,
2494 oscillation_damping=False, block_solve=True,
2495 pause_on_block_failure=False, line_search="stagnation"):
2496 r"""
2497 Solve the network.
2498
(...) 2594 documentation at tespy.readthedocs.io in the section "TESPy modules".
2595 """
-> 2596 self.presolve(
2597 mode, init_path=init_path, design_path=design_path,
2598 init_previous=init_previous, check=not init_only
2599 )
2601 if init_only:
2602 return
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2690, in Network.presolve(self, mode, init_path, design_path, init_previous, check)
2683 msg = (
2684 "Network information:\n"
2685 f" - Number of components: {len(self.comps)}\n"
2686 f" - Number of connections: {len(self.conns)}\n"
2687 )
2688 logger.debug(msg)
-> 2690 self._prepare_problem()
2691 self._presolve_pending = True
2693 if not check:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1050, in Network._prepare_problem(self)
1046 # this method will distribute units and set SI values from given values
1047 # and units
1048 self._transform_user_input_to_SI()
-> 1050 self._problem.build()
1052 # generic fluid property initialisation
1053 self._set_starting_values()
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:187, in Problem.build(self)
178 def build(self):
179 """Construct the problem from the prepared network.
180
181 - Assemble the structure matrix and the structure graph and reduce the
(...) 185 incidence.
186 """
--> 187 self._create_structure_matrix()
189 self.num_original_variables = len(self._variable_lookup)
190 self.num_original_equations = len(self._equation_set_lookup)
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:274, in Problem._create_structure_matrix(self)
266 sum_eq = self._preprocess_network_parts(self.network.user_defined_eq.values(), sum_eq)
268 self.structure_graph = StructureGraph(
269 self._structure_matrix, self._rhs,
270 self._variable_lookup, self._equation_set_lookup,
271 self._equation_set_origin
272 )
273 _linear_dependencies = (
--> 274 self.structure_graph.find_linear_dependent_variables()
275 )
276 _linear_dependent_variables = [
277 var for linear_dependents in _linear_dependencies
278 for var in linear_dependents["variables"]
279 ]
280 # variables without any affine partner become singleton groups
281 # referencing themselves: every variable owns a reference
282 # container this way and no consumer has to distinguish grouped
283 # from ungrouped variables
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/structure.py:198, in StructureGraph.find_linear_dependent_variables(self)
196 cycle = self.find_cycle()
197 if cycle is not None:
--> 198 self.raise_error_if_cycle(cycle)
200 adjacency_list = self.affine_adjacency
201 eq_idx = self.edge_eq_idx
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/structure.py:180, in StructureGraph.raise_error_if_cycle(self, cycle)
174 eq_str = ", ".join(f"{lbl}.{eq}" for lbl, eq in equations)
175 msg = (
176 "A circular dependency has been detected. This overdetermines the problem.\n"
177 f" Variables: {var_str}\n"
178 f" Equations: {eq_str}"
179 )
--> 180 raise hlp.TESPyNetworkError(msg)
TESPyNetworkError: A circular dependency has been detected. This overdetermines the problem.
Variables: c0 (m), c1 (m), c2 (m), c3 (m), c4 (m)
Equations: c1.m_ref, compressor.mass_flow_constraints, condenser.mass_flow_constraints, evaporator.mass_flow_constraints, valve.mass_flow_constraints
A last error that might occur is specification of properties that determine the same variable, e.g. the c2 pressure as the evaporation pressure is already determined from the saturation temperature and superheating.
c1.set_attr(m=None)
c2.set_attr(p=10) # p has already been set!
nw.solve("design")
---------------------------------------------------------------------------
TESPyNetworkError Traceback (most recent call last)
Cell In[29], line 3
1 c1.set_attr(m=None)
2 c2.set_attr(p=10) # p has already been set!
----> 3 nw.solve("design")
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2596, in Network.solve(self, mode, init_path, design_path, max_iter, min_iter, init_only, init_previous, use_cuda, print_results, robust_relax, skip_postprocess, oscillation_damping, block_solve, pause_on_block_failure, line_search)
2491 def solve(self, mode, init_path=None, design_path=None,
2492 max_iter=50, min_iter=2, init_only=False, init_previous=True,
2493 use_cuda=False, print_results=True, robust_relax=False, skip_postprocess=False,
2494 oscillation_damping=False, block_solve=True,
2495 pause_on_block_failure=False, line_search="stagnation"):
2496 r"""
2497 Solve the network.
2498
(...) 2594 documentation at tespy.readthedocs.io in the section "TESPy modules".
2595 """
-> 2596 self.presolve(
2597 mode, init_path=init_path, design_path=design_path,
2598 init_previous=init_previous, check=not init_only
2599 )
2601 if init_only:
2602 return
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:2690, in Network.presolve(self, mode, init_path, design_path, init_previous, check)
2683 msg = (
2684 "Network information:\n"
2685 f" - Number of components: {len(self.comps)}\n"
2686 f" - Number of connections: {len(self.conns)}\n"
2687 )
2688 logger.debug(msg)
-> 2690 self._prepare_problem()
2691 self._presolve_pending = True
2693 if not check:
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/networks/network.py:1050, in Network._prepare_problem(self)
1046 # this method will distribute units and set SI values from given values
1047 # and units
1048 self._transform_user_input_to_SI()
-> 1050 self._problem.build()
1052 # generic fluid property initialisation
1053 self._set_starting_values()
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:199, in Problem.build(self)
192 msg = (
193 f"Original problem: {self.num_original_variables} variables and "
194 f"{self.num_original_equations} equations, of which {num_affine} "
195 "equations were consumed by the affine variable elimination."
196 )
197 logger.debug(msg)
--> 199 self._presolve()
201 # counted only now: during the structure matrix assembly the
202 # specification and variable flags of the containers are transient,
203 # e.g. propagated fluid compositions read as set while their
204 # variable fractions are only marked during the presolving
205 self.num_specified_variables = 0
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/solver/problem.py:536, in Problem._presolve(self)
532 for c in to_check:
533 # cleared here, not in _presolve: custom connection classes are
534 # not required to know about the log
535 c._presolve_determinations = []
--> 536 self._presolved_equations += c._presolve()
537 for determination in c._presolve_determinations:
538 self._presolve_log.append({
539 "round": rounds,
540 "kind": "combination",
(...) 544 "requires": determination["requires"],
545 })
File ~/checkouts/readthedocs.org/user_builds/tespy/checkouts/stable/src/tespy/connections/connection.py:1700, in Connection._presolve(self)
1693 if num_specs > 2:
1694 msg = (
1695 "You have specified more than 2 parameters for the connection "
1696 f"{self.label} with a known fluid composition: "
1697 f"{', '.join(specifications)}. This overdetermines the state "
1698 "of the fluid."
1699 )
-> 1700 raise TESPyNetworkError(msg)
1702 presolved_equations = []
1704 if self.p.is_set:
TESPyNetworkError: You have specified more than 2 parameters for the connection c2 with a known fluid composition: p, T_dew, td_dew. This overdetermines the state of the fluid.
c2.set_attr(p=None)
Inspect reasons for linear dependency¶
You can also inspect the network after solve crashing. For this, we will construct a case where, we get this exact issue:
We fix heat output of condenser (having fixed motor electrical power already)
no specification of evaporator delta p
The block decomposition is able determine, that the problem is structurally singular.
condenser.set_attr(Q=-350)
evaporator.set_attr(dp=None)
nw.solve("design")
The problem is structurally singular, block-wise solving is not possible.
Structural analysis - the problem contains an under-determined part (1 variable constrained by 0 equations) and an over-determined part (3 equations competing for 2 variables).
Use nw.print_structural_analysis() for the affected equations and variables. If the structural defect stems from an incomplete dependency declaration of a custom equation, the simultaneous solution can still be attempted with nw.solve(mode, block_solve=False).
The solver reports that the problem is structurally singular although the parameter count matches. One part of the model is over-determined while another part is under-determined at the same time. The structural analysis prints both:
nw.print_structural_analysis()
Under-determined part - the following variables cannot be determined by the involved equations:
Variables: p2
Involved equations:
Over-determined part - the following equations compete for the involved variables:
Equations: compressor.energy_connector_balance, compressor.eta_s, condenser.Q
Involved variables: h0, m1
We can see the same looking at the actual variables and the equations associated with them separately:
nw.print_variables()
Variables after presolving (3 total):
# Property Represents
--- ---------- --------------------------------------
0 h c3 (h)
1 m c2 (m), c3 (m), c1 (m), c4 (m), c0 (m)
2 p c0 (p), c1 (p)
The under-determined variable p2 represents the pressures around the
evaporator: with its pressure drop specification removed, no equation
determines that pressure level anymore, while the condenser heat transfer
competes with the compressor equations for enthalpy and mass flow.
nw.print_equations_with_dependents()
Equations with dependent variables (3 total):
Eq# Object Equation Dependent variables
----- ---------- ------------------------ ---------------------
0 compressor energy_connector_balance h0, m1
1 compressor eta_s h0
2 condenser Q h0, m1
nw.print_incidence_matrix(block_order=True)
Incidence matrix:
Block p2 h0 m1
------- ----------------------------------- ---- ---- ----
1 compressor.energy_connector_balance - X X
compressor.eta_s - X -
condenser.Q - X X
nw.print_blocks()
Block lower triangular decomposition (2 blocks):
# Kind Needs Equations Variables
--- --------------- ------- ------------------------------------------------------------------ -----------
0 underdetermined p2
1 overdetermined compressor.energy_connector_balance, compressor.eta_s, condenser.Q h0, m1
A specification can also be numerically impossible while being structurally perfectly sound. In that case the structural analysis cannot detect the issue. Just a normal HeatExchanger is sufficient to show this:
from tespy.components import Source, Sink, HeatExchanger
nw = Network()
nw.units.set_defaults(
temperature="°C",
pressure="bar",
pressure_difference="bar"
)
so1 = Source("source 1")
so2 = Source("source 2")
si1 = Sink("sink 1")
si2 = Sink("sink 2")
heatex = HeatExchanger("heatexchanger")
c1 = Connection(so1, "out1", heatex, "in1", label="c1")
c2 = Connection(heatex, "out1", si1, "in1", label="c2")
d1 = Connection(so2, "out1", heatex, "in2", label="d1")
d2 = Connection(heatex, "out2", si2, "in1", label="d2")
nw.add_conns(c1, c2, d1, d2)
Now we could make a specification that is impossible but hard to catch as being a setup problem: We set a minimum terminal temperature difference of 25 K but at the same time fix the temperature at hot side outlet and cold side inlet (leading to a temperature difference of 20 K).
c1.set_attr(fluid={"air": 1}, T=200, p=1, m=5)
c2.set_attr(T=110)
d1.set_attr(fluid={"water": 1}, T=90, p=1)
heatex.set_attr(dp1=0, dp2=0, ttd_min=25)
nw.solve("design")
Block 0 did not converge, solving remaining 2 blocks simultaneously.
Cause: no acceptance within the iteration budget of 50 iterations, the last scaled residual is 5.00e+00
Equations: heatexchanger.ttd_min
Variables: h0
block 0 | scalar | iterations: 92 | residual: 5.00e+00 | heatexchanger.ttd_min
iter | residual | progress | massflow | pressure | enthalpy | fluid | energy | component
-------+------------+------------+------------+------------+------------+------------+------------+------------
1 | 8.37e-02 | 15 % | 1.10e-01 | 0.00e+00 | 1.97e+04 | 0.00e+00 | 0.00e+00 | 0.00e+00
2 | 5.00e+00 | 0 % | 8.91e-04 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
3 | 5.00e+00 | 0 % | 3.83e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
4 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
5 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
6 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
7 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
8 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
9 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
10 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
11 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
12 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
13 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
14 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
15 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
16 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
17 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
18 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
19 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
20 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
21 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
22 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
23 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
24 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
25 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
26 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
27 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
28 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
29 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
30 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
31 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
32 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
33 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
34 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
35 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
36 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
37 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
38 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
39 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
40 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
41 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
42 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
43 | 8.37e-02 | 15 % | 1.10e-01 | 0.00e+00 | 1.97e+04 | 0.00e+00 | 0.00e+00 | 0.00e+00
44 | 5.00e+00 | 0 % | 8.91e-04 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
45 | 5.00e+00 | 0 % | 3.83e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
46 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
47 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
48 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
49 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
50 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
51 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
52 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
53 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
54 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
55 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
56 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
57 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
58 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
59 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
60 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
61 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
62 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
63 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
64 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
65 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
66 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
67 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
68 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
69 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
70 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
71 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
72 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
73 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
74 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
75 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
76 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
77 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
78 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
79 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
80 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
81 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
82 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
83 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
84 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
85 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
86 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
87 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
88 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
89 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
90 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
91 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
92 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
block 0 | remainder | iterations: 92 | residual: 5.00e+00 | 2 equations
The remaining system did not converge either, restarting with the simultaneous solution of the full system from its initial state.
iter | residual | progress | massflow | pressure | enthalpy | fluid | energy | component
-------+------------+------------+------------+------------+------------+------------+------------+------------
1 | 8.37e-02 | 15 % | 1.10e-01 | 0.00e+00 | 1.97e+04 | 0.00e+00 | 0.00e+00 | 0.00e+00
2 | 5.00e+00 | 0 % | 8.91e-04 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
3 | 5.00e+00 | 0 % | 3.83e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
4 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
5 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
6 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
7 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
8 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
9 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
10 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
11 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
12 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
13 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
14 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
15 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
16 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
17 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
18 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
19 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
20 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
21 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
22 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
23 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
24 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
25 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
26 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
27 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
28 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
29 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
30 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
31 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
32 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
33 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
34 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
35 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
36 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
37 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
38 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
39 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
40 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
41 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
42 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
43 | 8.37e-02 | 15 % | 1.10e-01 | 0.00e+00 | 1.97e+04 | 0.00e+00 | 0.00e+00 | 0.00e+00
44 | 5.00e+00 | 0 % | 8.91e-04 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
45 | 5.00e+00 | 0 % | 3.83e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
46 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
47 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
48 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
49 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
50 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
51 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
52 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
53 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
54 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
55 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
56 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
57 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
58 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
59 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
60 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
61 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
62 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
63 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
64 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
65 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
66 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
The calculation did not converge, the last scaled residual is 5.00e+00 (heatexchanger: ttd_min).
Possible reasons include:
- fluid properties moving outside the valid range of the property database (consider adjusting p_range or h_range),
- an impossible constraint that can never be satisfied
- bad starting values causing the Newton solver to diverge.
Use nw.print_residuals() to identify which equations have the largest residuals.
67 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
68 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
69 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
70 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
71 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
72 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
73 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
74 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
75 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
76 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
77 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
78 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
79 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
80 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
81 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
82 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
83 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
84 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
85 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
86 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
87 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
88 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
89 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
90 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
91 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
92 | 5.00e+00 | 0 % | 3.85e-07 | 0.00e+00 | 5.00e+00 | 0.00e+00 | 0.00e+00 | 0.00e+00
Total iterations: 92, Calculation time: 2.34 s, Iterations per second: 39.28
Such an impossible specification leads to non-convergence. The block-wise
solution process localizes the problem: the first failing block names the
ttd_min equation, and the final message quotes the equation with the largest
scaled residual. The residuals show that the energy balance is satisfied while
ttd_min cannot fall below a residual of 5, which is exactly the 5 K by which
the specification is infeasible:
nw.print_residuals()
Residuals per equation (2 total, sorted by scaled magnitude):
Eq# Object Equation Scaled Residual
----- ------------- -------------------------- --------- ----------
1 heatexchanger ttd_min 5.000e+00 5.000e+00
0 heatexchanger energy_balance_constraints 6.488e-13 -1.925e-06
Next steps¶
The solver section documents the full solution process and all inspection methods shown here. For debugging the solution process itself in the block decomposition, pausing at a failed block and correcting starting values interactively, see the advanced debugging tutorial.