void getInverseMatrix(const CellIter& c,
FullMatrix<Scalar,SP,FortranOrdering>& Binv) const
{
// Binv = (N*lambda*K*N' + t*diag(A)*(I - Q*Q')*diag(A))/vol
// ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^
// precomputed: n_ precomputed: second_term_
// t = 6/dim * trace(lambda*K)
int ci = c->index();
int nf = Binv.numRows();
ImmutableFortranMatrix n(nf, dim, &n_[ci][0]);
ImmutableFortranMatrix t2(nf, nf, &second_term_[ci][0]);
Binv = t2;
ImmutableFortranMatrix lambdaK(dim, dim, lambdaK_.data());
SharedFortranMatrix T2(nf, dim, &t2_[0]);
// T2 <- N*lambda*K
matMulAdd_NN(Scalar(1.0), n, lambdaK, Scalar(0.0), T2);
// Binv <- (T2*N' + t*Binv) / vol(c)
// == (N*lambda*K*N' + t*(diag(A) * (I - Q*Q') * diag(A))) / vol(c)
//
// where t = 6/d * TRACE(lambda*K) (== 2*TRACE(lambda*K) for 3D).
//
Scalar t = Scalar(6.0) * trace(lambdaK) / dim;
matMulAdd_NT(Scalar(1.0) / c->volume(), T2, n,
t / c->volume(), Binv );
}
