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/*
ARPACK++ v1.2 2/20/2000
c++ interface to ARPACK code.
MODULE DCMatrxA.h
Function template for the nx*nx by nx*nx block tridiagonal matrix
| T -I |
|-I T -I |
OP = | -I T |
| ... -I|
| -I T|
derived from the standard central difference discretization
of the 2 dimensional convection-diffusion operator
-(Laplacian u) + rho*(du/dx)
on a unit square with zero boundary conditions.
T is a nx by nx tridiagonal matrix with DD on the diagonal,
DL on the subdiagonal, and DU on the superdiagonal.
ARPACK Authors
Richard Lehoucq
Danny Sorensen
Chao Yang
Dept. of Computational & Applied Mathematics
Rice University
Houston, Texas
*/
#ifndef DCMATRXA_H
#define DCMATRXA_H
#include "arcomp.h"
#include "blas1c.h"
template<class ARFLOAT, class ARINT>
void CompMatrixA(ARINT nx, ARINT& n, arcomplex<ARFLOAT>* &A)
{
ARINT i, j;
arcomplex<ARFLOAT> h, h2, dd, dl, du, df;
// Defining constants.
const arcomplex<ARFLOAT> half(0.5,0.0);
const arcomplex<ARFLOAT> one(1.0,0.0);
const arcomplex<ARFLOAT> four(4.0,0.0);
const arcomplex<ARFLOAT> rho(1.0e2,0.0);
h = one/arcomplex<ARFLOAT>((ARFLOAT)(nx+1),0);
h2 = h*h;
df = -(one/h2);
dd = four/h2;
dl = df - half*rho/h;
du = df + half*rho/h;
// Defining the dimension of the problem.
n = nx*nx;
// Creating output vector A.
A = new arcomplex<ARFLOAT>[n*n];
for (i=0; i<n*n; i++) A[i] = arcomplex<ARFLOAT>(0.0, 0.0);
for (i=0, j=0; i<n; i++, j+=n+1) {
if (i>=nx) A[j-nx] = df;
if (i%nx) A[j-1] = du;
A[j] = dd;
if ((i+1)%nx) A[j+1] = dl;
if (i<(n-nx)) A[j+nx] = df;
}
} // CompMatrixA.
#endif // DCMATRXA_H
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