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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE BSMatrxA.h
Function template for the matrix
| T -I |
|-I T -I |
A = | -I T |
| ... -I|
| -I T|
derived from the standard central difference discretization of the
2-dimensional Laplacian on the unit square with zero Dirichlet
boundary conditions.
Matrix A is generated in symmetric band format, which means that
only the main diagonal and the lower or the upper band of the
matrix are stored.
ARPACK Authors
Richard Lehoucq
Danny Sorensen
Chao Yang
Dept. of Computational & Applied Mathematics
Rice University
Houston, Texas
*/
#ifndef BSMATRXA_H
#define BSMATRXA_H
#include <math.h>
template<class ARFLOAT, class ARINT>
void BandMatrixA(ARINT nx, ARINT& n, ARINT& nD, ARFLOAT* &A, char uplo='L')
{
// Defining internal variables.
ARINT i, j, lda;
ARFLOAT h2, df, dd;
// Defining constants.
h2 = 1.0/(ARFLOAT(nx+1)*ARFLOAT(nx+1));
dd = 4.0/h2;
df = -1.0/h2;
// Defining the number of columns and the upper or the lower bandwidth.
n = nx*nx;
nD = nx;
// Creating output vector A.
lda = nD+1;
A = new ARFLOAT[n*lda];
// Filling A with zeros.
for (j=0; j<(n*lda); j++ ) A[j] = (ARFLOAT)0.0;
// Creating matrix A.
if (uplo == 'L') {
for (i=0, j=0; i<n; i++, j+=lda) {
A[j] = dd;
if ((i+1)%nx) A[j+1] = df;
if (i<(n-nx)) A[j+nx] = df;
}
}
else {
for (i=0, j=nD; i<n; i++, j+=lda) {
if (i>=nx) A[j-nx] = df;
if (i%nx) A[j-1] = df;
A[j] = dd;
}
}
} // BandMatrixA.
#endif // BSMATRXA_H
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