How to find gradient of a variable in 3D mapped finite element domain

[Stacky]

Hello,
I know the value of a field variable in a 3d mapped finite element mesh. Can anyone suggest an effective method/methods to find its gradient throughout the mesh.

 

[Vadar2012]

We're going to need more information than that mate. What program are you using etc.

 

[Stacky]

Yeah, I am not using any readymade sofware, I am writing a code in c language. Calculating gradient of a variable is a part of solving a differential equation through finite element. I am using mapped 3d hexahedral finite element. I am just enquiring an effective approach/method to calculate the gradient of a variable.

 

[Vadar2012]

Ah that makes it easier. I've done it before, but in Matlab. Was a long time ago though. Let me refresh my memory.