Reduced minimum size for sparse linear and nonlinear solvers

[casella]

See discussion in ticket #6342

[AnHeuermann]

LGTM

[AnHeuermann]

@casella Just in case you are not aware: You can fix the failing tests automatically by running e.g.

Andreas@DESKTOP-OSJIVA0 MINGW64 /D/workspace/OpenModelica/testsuite/simulation/modelica/linear_system
# ../../../rtest -b NPendulum40.mos

with MINGW, but check if it didn't change to much. You can find rtest in OpenModelica/testsuite.

[casella]

@casella Just in case you are not aware: You can fix the failing tests automatically by running e.g.

Andreas@DESKTOP-OSJIVA0 MINGW64 /D/workspace/OpenModelica/testsuite/simulation/modelica/linear_system
# ../../../rtest -b NPendulum40.mos

with MINGW, but check if it didn't change to much. You can find rtest in OpenModelica/testsuite.

Thank you for the info. I'd like to make sure that nothing actually got broken. Where exactly do I find the diff between the previous and actual test results? The log file is huge and I have some difficulties orienting myself in it.

[phannebohm]

Poke!

All tests look fine, they just need to be updated because the prints changed.
The the failing tests in clang and gcc are identical so it's only 10.

You can Ctrl+F for "diff says" after expanding the test to find its diff. Is that what you mean?

Equation mismatch: diff says:
--- /tmp/omc-rtest-unknown/simulation/modelica/others/EngineV6_output.mos_temp8063/equations-expected2021-07-03 01:27:06.547536970 +0000
+++ /tmp/omc-rtest-unknown/simulation/modelica/others/EngineV6_output.mos_temp8063/equations-got2021-07-03 01:29:12.989324966 +0000
@@ -7,12 +7,20 @@
 ""
 There have been 1345 SCCs and now there are 686 SCCs.
 record SimulationResult
 resultFile = "EngineV6_output_res.mat",
 simulationOptions = "startTime = 0.0, stopTime = 1.01, numberOfIntervals = 500, tolerance = 1e-06, method = 'dassl', fileNamePrefix = 'EngineV6_output', options = '', outputFormat = 'mat', variableFilter = '.*', cflags = '', simflags = ''",
-messages = "LOG_SUCCESS       | info    | The initialization finished successfully without homotopy method.
+messages = "stdout            | info    | Using sparse solver for linear system 6,
+| | |       | because density of 0.176 remains under threshold of 0.200 and size of 27 exceeds threshold of 10.
+| | |       | The maximum density and the minimal system size for using sparse solvers can be specified
+| | |       | using the runtime flags '<-lssMaxDensity=value>' and '<-lssMinSize=value>'.
+stdout | info    | Using sparse solver for linear system 13,
+| | |       | because density of 0.155 remains under threshold of 0.200 and size of 25 exceeds threshold of 10.
+| | |       | The maximum density and the minimal system size for using sparse solvers can be specified
+| | |       | using the runtime flags '<-lssMaxDensity=value>' and '<-lssMinSize=value>'.
+LOG_SUCCESS | info    | The initialization finished successfully without homotopy method.
 LOG_SUCCESS       | info    | The simulation finished successfully.
 "
 end SimulationResult;
 ""
-561.4775584669958
+561.4775584670217
 ""
Equation mismatch: omc-diff says:
Failed 'L' 's'
Line 12: Text differs:
expected: messages = "LOG_SUCCESS       | info    | The initialization finished successfully without homotopy method.
got:      messages = "stdout            | info    | Using sparse solver for linear system 

[casella]

@phannebohm, this PR was a drastic solution, basically turning off tearing completely for linear systems. The idea was to use sparse solvers instead. The problem is that if you don't enable them explicitly, they won't be used, so the performance will become a lot worse. So, this PR is not really the ideal solution.

I think we should first check why strict tearing is not working as expected, see #6196 and fix that.