workaround, make the opaque struct MatrixElement partially visible
this struct is private to the `sparse' world,
and lives in "maths/sparse/spdefs.h"
which can't be included here, because
it is incompatible to the rest of ngspice.
this is the same problem as in
ciderlib/oned/oneprint.c
ciderlib/twod/twoprint.c
dwarning
rlar
Francesco Lannutti
pnenzi