C++ for Scientists - Technische Universität Dresden

14.1. COMPUTING AN EIGENFUNCTION OF THE POISSON EQUATION 271
0.45
0.4
0.35
0.3
0.25
0.2
0.15
"x.out"
0.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Figure 14.1: First eigenvector of the 1D Poisson operator
int main() {
typedef glas::dense vector v type ;
int n = 10 ;
v type x( n ) ;
glas::random seed seed ;
glas::random( x, seed ) ;
v type d( n ) ; std::fill( begin(d), end(d), 2.0 ) ;
v type e( n−1 ) ; std::fill( begin(e), end(e), −1.0 ) ;
solve< v type, v type > solver( d, e ) ;
athens::inverse iteration( solver, x, 100, lambda ) ;
std::cout ≪ ”lambda = ” ≪ lambda ≪ std::endl ;
std::ofstream xf( ”x.out” ) ;
for ( int i=0; i plot "x.out" w l
gnuplot>