lnmatrxd.h

ARPACK is a collection of Fortran77 subroutines designed to solve large scale eigenvalue problems.

/*
   ARPACK++ v1.0 8/1/1997
   c++ interface to ARPACK code.

   MODULE LNMatrxD.h
   Function template for the mass matrix formed by using piecewise 
   linear elements on [0, 1].

   ARPACK Authors
      Richard Lehoucq
      Danny Sorensen
      Chao Yang
      Dept. of Computational & Applied Mathematics
      Rice University
      Houston, Texas
*/

#ifndef LNMATRXD_H
#define LNMATRXD_H

template<class FLOAT, class INT>
void MassMatrix(INT n, INT& nnz, FLOAT* &A, INT* &irow, INT* &pcol)
{

  INT   i,j;
  FLOAT diag, sub;

  // Defining constants.

  sub  = 1.0/FLOAT(n+1);
  diag = 4.0/FLOAT(n+1);

  // Defining the number of nonzero matrix elements.

  nnz = 3*n-2;

  // Creating output vectors.

  A    = new FLOAT[nnz];
  irow = new INT[nnz];
  pcol = new INT[n+1];

  // Filling A, irow and pcol.

  pcol[0] = 0;
  j = 0;
  for (i=0; i!=n; i++) {
    if (i != 0) {
      irow[j] = i-1;
      A[j++]  = sub;
    }
    irow[j] = i;
    A[j++]  = diag;
    if (i != (n-1)) {
      irow[j] = i+1;
      A[j++]  = sub;
    }
    pcol[i+1] = j;
  }

} // MassMatrix.

#endif // LNMATRXD_H