Example 2: Integral of exp(-x) from 0 to infinity

The integral \int_0^\infty e^{-x} \, dx is computed and compared to its expected value. 
import com.imsl.math.*;

public class QuadratureEx2 {
    public static void main(String args[]) {
        
        Quadrature.Function fcn = new Quadrature.Function() {
            public double f(double x) {
                return Math.exp(-x);
            }
        };
        
        Quadrature q = new Quadrature();
        double result = q.eval(fcn, 0.0, Double.POSITIVE_INFINITY);
        
        double expect = 1.;
        System.out.println("result = "+result);
        System.out.println("expect = "+expect);
    }
}

Output

result = 0.999999999999999
expect = 1.0
Link to Java source.