Hello. My field variable is
 

Hello.

My field variable is a scalar (concentration). I need to calculate the
flux (which is -grad(C)) across one of the patches. I could use
patchIntegrate utility for integration over the patch but I need
gradient field for that.

foamCalc utility can calculate div(U) but only for vector fields. Is
there a way to automatically calculate the field of gradients having
the field of scalar?

Thank you for your help,
Eugene