Mass matrix
= Mass matrix
{title2=$M_{ij}=\int_\Omega\phi_i\phi_j$}
The mass matrix is the <Gram matrix> of a <finite element> basis in the <L2 inner product>. Its coefficient <quadratic form> is the squared <L2 norm> of the represented trial function, so it is a <positive-definite matrix> for a linearly independent basis.