Eigenvalue Calculation using Python Programming Filter

Hi,

I want to calculate the principal strains of a 3D data. Here’s my workflow:

1. Use `ComputeDerivatives` to get the strain tensor from the displacement.
2. Use ‘Programming Filter’ and the code is from Paraview Wiki:

https://www.paraview.org/Wiki/PrincipleStrainPython

``````import numpy as np
from vtk.numpy_interface import algorithms as algs
from paraview.vtk.numpy_interface import dataset_adapter as dsa

def process_composite_dataset(input0):
# Pick up input arrays
xxar = input0.CellData["Strain_0"]
xyar = input0.CellData["Strain_1"]
zxar = input0.CellData["Strain_6"]
yyar = input0.CellData["Strain_4"]
yzar = input0.CellData["Strain_7"]
zzar = input0.CellData["Strain_8"]

#print `xxar`
#print len(xxar.Arrays)

# Set output arrays to same type as input array.
# Do a multiply to make sure we don't just have a
#   pointer to the original.
outarray0 = xxar*0.5
outarray1 = xxar*0.5
outarray2 = xxar*0.5

# Run a for loop over all blocks
numsubarrays = len(xxar.Arrays)
for ii in range(0, numsubarrays):

# pick up input arrays for each block.
xxarsub = xxar.Arrays[ii]
xyarsub = xyar.Arrays[ii]
zxarsub = zxar.Arrays[ii]
yyarsub = yyar.Arrays[ii]
yzarsub = yzar.Arrays[ii]
zzarsub = zzar.Arrays[ii]

#print `xxarsub`

# Transpose and calculate the principle strain.
strain = np.transpose(
np.array(
[ [xxarsub, xyarsub, zxarsub],
[xyarsub, yyarsub, yzarsub],
[zxarsub, yzarsub, zzarsub] ] ),
(2,0,1))

principal_strain = np.linalg.eigvalsh(strain)

# Move principle strain to temp output arrays for this block
outarray0.Arrays[ii] = principal_strain[:,0]
outarray1.Arrays[ii] = principal_strain[:,1]
outarray2.Arrays[ii] = principal_strain[:,2]

#ps0 = principal_strain[:,0]
#print "ps0 len: " + str(len(ps0))

# Finally, move the temp arrays to output arrays
output.CellData.append(outarray0, "principal_strain_0")
output.CellData.append(outarray1, "principal_strain_1")
output.CellData.append(outarray2, "principal_strain_2")
``````

However, when I clicked “Apply”, this Error showed up:

``````ValueError: axes don't match array
Traceback (most recent call last):
File "<string>", line 22, in <module>
File "<string>", line 123, in RequestData
File "<string>", line 95, in process_unstructured_dataset
File "<__array_function__ internals>", line 5, in transpose
File "C:\Program Files\ParaView 5.10.1-MPI-Windows-Python3.9-msvc2017-AMD64\bin\Lib\site-packages\numpy\core\fromnumeric.py", line 660, in transpose
return _wrapfunc(a, 'transpose', axes)
File "C:\Program Files\ParaView 5.10.1-MPI-Windows-Python3.9-msvc2017-AMD64\bin\Lib\site-packages\numpy\core\fromnumeric.py", line 57, in _wrapfunc
return bound(*args, **kwds)...
``````

Does anyone know what’s wrong here?

Thanks,
Gening