# [Paraview] Calculation of a scalar (density) gradient - For a node centred solution

Amit Roghelia amitroghs at yahoo.com
Mon Dec 3 06:16:15 EST 2012

```Dear All,
I have a node centered solution for my problem using an unstructured hybrid (tetra, prism) grid. And so I have the value of density (only one value - as it scalar) at each node location in the ASCII file of the result.

I am calculating the density gradient using the Compute Derivative option and I get the magnitude and three gradients (in x , y and z direction).

My question is how the three gradients (in x, y and z direction) are calculated in a node -centered unstructured grid ?

Is it right that first, the cell centered value (absolute density) is calculated from the node centers via interpolation and then the gradients from the cell centered value?

I could find the reference (below) for a hexahedral mesh, but not for an unstructured mesh.
http://www.vtk.org/doc/release/4.0/html/classvtkHexahedron.html#a16

Regards,

Amit
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