how to calculate the magnitude (module) of a gradient
Goodmorning, I'm working in the frame of phase field models for solidification.
I've to solve a transport equation for the phase field (1 in one phase,1 in the other one and a smooth passage atthe interface). The equation i've to solve present the module of the gradient grad f (the vector magnitude): df/dt+V*grad f=a*[ laplacian f+f*(1f)/bgrad f div [ grad f/grad f]] with a,b parameters (or constants). how can I calculate the grad f term when I want to solve the equation? I tried that way: 1) grad f ==== mag(fvc::grad(phase)) where phase is my "f" 2)otherwise I also tried to first define: volVectorField gradphase = fvc::grad(phase); and after grad f ==== mag(gradphase) are they equivalent? or at least, is one correct? Thank you in advance, I'm quite new in openfoam (and in c++). 
Hi
I think they are equivalent but what is "===="? 
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