MC63: Generate an element assembly ordering for a frontal solver

This subroutine uses a variant of Sloan’s algorithm to generate an element assembly ordering that is efficient when subsequently used with a frontal solver (for example, the packages MA42 and MA62). The number of floating-point operations and the storage required by a frontal solver for an unassembled finite-element matrix are dependent upon the order in which the elements are assembled; the variation in the performance of different element orderings can be significant. The assembly ordering obtained by MC63 is designed to reduce the maximum and root-mean-square (r.m.s.) wavefronts and the profile, which in turn reduce storage requirements and computation times for the frontal solver. Only the pattern of the finite elements is used.