How can I compute inductance for cases where LMATRIX is not applicable?
You can use the magnetic energy, equal to 1/2 Li^2, which is computed as follows:
smult,Energy,b_sum,h_sum,0.5 ! energy density = BH/2
smult,Energy,Energy,volu, ! multiply by volume and symmetry factor
ssum ! sum over the elements. Inductance = 2 x Energy / i^2