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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE LCMatrxB.h
Function template for the tridiagonal matrix derived from
the standard central difference of the 1-d convection diffusion
operator u" + rho*u' on the interval [0, 1] with zero
Dirichlet boundary conditions.
ARPACK Authors
Richard Lehoucq
Danny Sorensen
Chao Yang
Dept. of Computational & Applied Mathematics
Rice University
Houston, Texas
*/
#ifndef LCMATRXB_H
#define LCMATRXB_H
#include "arcomp.h"
template<class ARFLOAT, class ARINT>
void CompMatrixB(ARINT n, arcomplex<ARFLOAT> rho, ARINT& nnz,
arcomplex<ARFLOAT>* &A, ARINT* &irow, ARINT* &pcol)
{
ARINT i, j;
arcomplex<ARFLOAT> dd, dl, du, s, h, h2;
// Defining constants.
const arcomplex<ARFLOAT> one( 1.0, 0.0);
const arcomplex<ARFLOAT> two( 2.0, 0.0);
h = one/arcomplex<ARFLOAT>((ARFLOAT)(n+1),0.0);
h2 = h*h;
s = rho/two;
dd = two/h2;
dl = -(one/h2) - s/h;
du = -(one/h2) + s/h;
// Defining the number of nonzero matrix elements.
nnz = 3*n-2;
// Creating output vectors.
A = new arcomplex<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) {
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;
}
} // CompMatrixB.
#endif // LCMATRXB_H
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