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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE LSMatrxA.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 LSMATRXA_H
#define LSMATRXA_H
#include <math.h>
template<class ARFLOAT, class ARINT>
void SymmetricMatrixA(ARINT nx, ARINT& n, ARINT& nnz, ARFLOAT* &A,
ARINT* &irow, ARINT* &pcol, 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 number of columns and nonzero elements of matrix.
n = nx*nx;
nnz = 3*n-2*nx;
// Creating output vectors.
A = new ARFLOAT[nnz];
irow = new ARINT[nnz];
pcol = new ARINT[n+1];
// Defining matrix A.
pcol[0] = 0;
i = 0;
if (uplo == 'U') {
for (j = 0; j < n; j++) {
if (j >= nx) {
A[i] = df; irow[i++] = j-nx;
}
if ((j%nx) != 0) {
A[i] = df; irow[i++] = j-1;
}
A[i] = dd; irow[i++] = j;
pcol[j+1] = i;
}
}
else {
for (j = 0; j < n; j++) {
A[i] = dd; irow[i++] = j;
if (((j+1)%nx) != 0) {
A[i] = df; irow[i++] = j+1;
}
if (j < n-nx) {
A[i] = df; irow[i++] = j+nx;
}
pcol[j+1] = i;
}
}
} // SymmetricMatrixA.
#endif // LSMATRXA_H
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