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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE LNMatrxC.h
Function template for the stiffness matrix obtained from
the finite element discretization of the 1-dimensional
convection diffusion operator d^2u/dx^2 + rho*(du/dx) on
the interval [0,1] with zero Dirichlet boundary condition
using linear elements.
ARPACK Authors
Richard Lehoucq
Danny Sorensen
Chao Yang
Dept. of Computational & Applied Mathematics
Rice University
Houston, Texas
*/
#ifndef LNMATRXC_H
#define LNMATRXC_H
template<class ARFLOAT, class ARINT>
void StiffnessMatrix(ARINT n, ARFLOAT rho, ARINT& nnz,
ARFLOAT* &A, ARINT* &irow, ARINT* &pcol)
{
ARINT i, j;
ARFLOAT dd, dl, du, s, h;
// Defining constants.
const ARFLOAT one = 1.0;
const ARFLOAT two = 2.0;
h = one/ARFLOAT(n+1);
s = rho/two;
dd = two/h;
dl = -one/h - s;
du = -one/h + s;
// Defining the number of nonzero matrix elements.
nnz = 3*n-2;
// Creating output vectors.
A = new ARFLOAT[nnz];
irow = new ARINT[nnz];
pcol = new ARINT[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++] = du;
}
irow[j] = i;
A[j++] = dd;
if (i != (n-1)) {
irow[j] = i+1;
A[j++] = dl;
}
pcol[i+1] = j;
}
} // StiffnessMatrix.
#endif // LNMATRXC_H
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