Model of a polyphase inductor providing a mutual inductance matrix model.
v[1] = L[1,1]*der(i[1]) + L[1,2]*der(i[2]) + ... + L[1,m]*der(i[m])
v[2] = L[2,1]*der(i[1]) + L[2,2]*der(i[2]) + ... + L[2,m]*der(i[m])
: : : :
v[m] = L[m,1]*der(i[1]) + L[m,2]*der(i[2]) + ... + L[m,m]*der(i[m])