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python calculator - laplacian(U) calculation

Hi everyone,
I am currently trying to evaluate through python calculator the laplacian of U, however such function only takes as input scalars. I wanted thus to write something similar to

Code:

laplacian(U_X)

however I cannot make it work, and I get this error message.

Code:

  File "/opt/paraviewopenfoam56/lib/python2.7/site-packages/paraview/calculator.py", line 192, in execute

    retVal = compute(inputs, expression, ns=variables)

  File "/opt/paraviewopenfoam56/lib/python2.7/site-packages/paraview/calculator.py", line 140, in compute

    retVal = eval(expression, globals(), mylocals)

  File "<string>", line 1, in <module>

NameError: name 'U_X' is not defined

Do you have any suggestion on how to evaluate such term?
Thanks in advance.

Nevermind, I figured it out, it is probably basic knowledge but I will explain anyway.
The syntax to extract the single component from the vector and evaluate the laplacian is

Code:

laplacian(U[:,0])