Discussion Forum

Dear all,
in the scope of research project, I'm checking out COMSOL's abilty of accessing external material models. There's an example code available via www.comsol.com/model/external-material-ac-dc-module-general-hb-bh-relation-32321 . What I'm trying to do now is to understand that referred example. I'm aware of what's happening during the interpolation routine, but I don't understand how the Jacobian Matrix is built:
// Write Jacobian of B with respect to H
if (normH>0) {
for (i=0; i<3; ++i) {
for (j=0; j<3; ++j) {
Jac[i*3+j] = dNormB*H[i]*H[j]/(normH*normEpsH)+normB*(-H[i]*H[j]/(normEpsH2*normEpsH)+(i==j ? 1.0/normEpsH : 0.0));
}
}
} else {
for (i=0; i<3; ++i) {
for (j=0; j<3; ++j) {
Jac[i*3+j] = (i==j ? dNormB : 0.0);
}
}
}
I know that a Jacobian Matrix contains the partial derivatives of a vector valued function, but I don't really understand the procedure in the code-snippet above. Can anyone help me out and explain it to me or post a link to a literature reference (with an explanation of the procedure)?


Thanks in advance and best regards

Michael