#include "petscmat.h" PetscErrorCode MatIsShell(Mat mat, PetscBool *flg)
| mat | - the matrix | 
| flg | - the boolean value | 
Notes: in the future, we should allow the object type name to be changed still using the MatShell data structure for other matrices (i.e. MATTRANSPOSEMAT, MATSCHURCOMPLEMENT etc)