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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE DSMatrxA.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.
ARPACK Authors
Richard Lehoucq
Danny Sorensen
Chao Yang
Dept. of Computational & Applied Mathematics
Rice University
Houston, Texas
*/
#ifndef DSMATRXA_H
#define DSMATRXA_H
#include <math.h>
template<class ARFLOAT, class ARINT>
void DenseMatrixA(ARINT nx, ARINT& n, ARFLOAT* &A, char uplo = 'L')
{
// Defining internal variables.
ARINT i, j;
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 dimension of A.
n = nx*nx;
// Creating matrix A.
A = new ARFLOAT[(n*n+n)/2];
for (i=0; i<(n*n+n)/2; i++) A[i]=0.0;
if (uplo == 'L') {
for (i=0, j=0; i<n; j+=(n-(i++))) {
A[j] = dd;
if (((i+1)%nx) != 0) {
A[j+1] = df;
}
if (i < n-nx) {
A[j+nx] = df;
}
}
}
else { // uplo = "U"
for (i=0, j=0; i<n; j+=(++i)) {
A[j+i] = dd;
if ((i%nx) != 0) {
A[j+i-1] = df;
}
if (i >= nx) {
A[j+i-nx] = df;
}
}
}
} // DenseMatrixA.
#endif // DSMATRXA_H
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