4.3.3.1 Generation of stiffness matrix.

Denote with $\widetilde{{\ensuremath{\color{red}\mathfrak{K}}}} \makebox[0pt]{}_i$ that part of the global stiffness matrix which matrix graph contains only connections from inner nodes ( $x \in \overline{\Omega} \makebox[0pt]{}_{h,i}\setminus \Gamma_{h,i}$) to nodes of the whole subdomain ( $x\in \overline{\Omega} \makebox[0pt]{}_{h,i}$), i.e, $\widetilde{{\ensuremath{\color{red}\mathfrak{K}}}} \makebox[0pt]{}_i$ is an accumulated rectangular matrix.
Other storage schemes are conceivably.