Error in FSI tutorials run with FEniCS

[IshaanDesai]

The following error is seen in OpenFOAM-FEniCS and SU2-FEniCS FSI tutorial for the perpendicular flap setup:

Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
Couldn't map 'f_1050' to a float, returning ufl object without evaluation.
terminate called after throwing an instance of 'pybind11::error_already_set'
  what():  RecursionError: maximum recursion depth exceeded while calling a Python object

At:
  /home/ishaan/.local/lib/python3.6/site-packages/ufl/core/operator.py(61): <genexpr>

[ishaan-ThinkPad-L440:17907] *** Process received signal ***
[ishaan-ThinkPad-L440:17907] Signal: Aborted (6)
[ishaan-ThinkPad-L440:17907] Signal code:  (-6)
[ishaan-ThinkPad-L440:17907] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x3efd0)[0x7fa7fe2acfd0]
[ishaan-ThinkPad-L440:17907] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7)[0x7fa7fe2acf47]
[ishaan-ThinkPad-L440:17907] [ 2] /lib/x86_64-linux-gnu/libc.so.6(abort+0x141)[0x7fa7fe2ae8b1]
[ishaan-ThinkPad-L440:17907] [ 3] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x9a257)[0x7fa7fa8a0257]
[ishaan-ThinkPad-L440:17907] [ 4] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xa5606)[0x7fa7fa8ab606]
[ishaan-ThinkPad-L440:17907] [ 5] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xa5671)[0x7fa7fa8ab671]
[ishaan-ThinkPad-L440:17907] [ 6] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xa5905)[0x7fa7fa8ab905]
[ishaan-ThinkPad-L440:17907] [ 7] /usr/lib/python3/dist-packages/dolfin/cpp.cpython-36m-x86_64-linux-gnu.so(+0x587f8)[0x7fa7fc7417f8]
[ishaan-ThinkPad-L440:17907] [ 8] python3(_PyCFunction_FastCallDict+0x35c)[0x566ddc]
[ishaan-ThinkPad-L440:17907] [ 9] python3[0x50a783]
[ishaan-ThinkPad-L440:17907] [10] python3(_PyEval_EvalFrameDefault+0x444)[0x50c1f4]
[ishaan-ThinkPad-L440:17907] [11] python3(_PyFunction_FastCallDict+0xf5)[0x509015]
[ishaan-ThinkPad-L440:17907] [12] python3[0x594b01]
[ishaan-ThinkPad-L440:17907] [13] python3(PyObject_Call+0x3e)[0x59fe1e]
[ishaan-ThinkPad-L440:17907] [14] python3[0x4b1eea]
[ishaan-ThinkPad-L440:17907] [15] python3[0x488370]
[ishaan-ThinkPad-L440:17907] [16] python3[0x59cb00]
[ishaan-ThinkPad-L440:17907] [17] python3(_PyEval_EvalFrameDefault+0x28bc)[0x50e66c]
[ishaan-ThinkPad-L440:17907] [18] python3[0x507f24]
[ishaan-ThinkPad-L440:17907] [19] python3(PyEval_EvalCode+0x23)[0x50b053]
[ishaan-ThinkPad-L440:17907] [20] python3[0x634dd2]
[ishaan-ThinkPad-L440:17907] [21] python3(PyRun_FileExFlags+0x97)[0x634e87]
[ishaan-ThinkPad-L440:17907] [22] python3(PyRun_SimpleFileExFlags+0x17f)[0x63863f]
[ishaan-ThinkPad-L440:17907] [23] python3(Py_Main+0x591)[0x6391e1]
[ishaan-ThinkPad-L440:17907] [24] python3(main+0xe0)[0x4b0dc0]
[ishaan-ThinkPad-L440:17907] [25] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7fa7fe28fb97]
[ishaan-ThinkPad-L440:17907] [26] python3(_start+0x2a)[0x5b26fa]
[ishaan-ThinkPad-L440:17907] *** End of error message ***

• This is also mentioned here.
• Running some experiments show that the error occurs if the simulation is run for >= 5 secs (500 steps with a time-window size of 1e-2).
• The critical line appears to be:

  what():  RecursionError: maximum recursion depth exceeded while calling a Python object
  
  At:
    /home/ishaan/.local/lib/python3.6/site-packages/ufl/core/operator.py(61): <genexpr>
  

  It is known that in python the number of permissible recursion levels for a recursive function call are locked at 999. For this case it is still unclear from where the recursive call is originating.
• The ufl package mentioned here is a package from the FEniCS Project.

[BenjaminRodenberg]

Some "good news" on this error: I also get it for the HT tutorial. Why good?

• Easier and quicker to run (removing error checks and setting the QN tolerance large makes it even quicker)
• Error is not specifically related to PointSource

Note that I observed the error after 331 timesteps. Both for FSI/flap_perp/OpenFOAM-FEniCS and HT/partitioned-heat/fenics-fenics.

[BenjaminRodenberg]

The following script can be used to reproduce the error:

import fenics

t = 0
dt = fenics.Constant(0)
dt.assign(0.001)

while float(t) < 1:
    print(float(t))
    t += dt

We have to be careful, when summing up FEniCS Constants. Doing something like t += dt in the user code is clearly wrong usage that we should fix in the solver. Let's hope that we are not doing something similar inside the adapter...

The code above can be fixed, by simply converting dt to float:

    t += float(dt)