package com.nr.test.test_chapter17;
import static com.nr.test.NRTestUtil.maxel;
import static com.nr.test.NRTestUtil.vecsub;
import static org.junit.Assert.fail;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.nr.ode.DerivativeInf;
import com.nr.ode.Odeint;
import com.nr.sf.Bessjy;
public class Test_rk4 {
@Before
public void setUp() throws Exception {
}
@After
public void tearDown() throws Exception {
}
@Test
public void test() {
int i,nvar=4;
double x,h,sbeps;
double[] y= new double[nvar],dydx= new double[nvar],yout= new double[nvar],yexp= new double[nvar];
boolean localflag, globalflag=false;
// Test rk4
System.out.println("Testing rk4");
x=1.0;
h=0.1;
Bessjy bess=new Bessjy();
for (i=0;i<nvar;i++) {
y[i]=bess.jn(i,x);
yexp[i]=bess.jn(i,x+h);
}
rk4_derivs(x,y,dydx);
RK4_derivs rk4_derivs = new RK4_derivs();
Odeint.rk4(y,dydx,x,h,yout,rk4_derivs);
for (i=0;i<nvar;i++)
System.out.printf("%f %f\n", yout[i], yexp[i]);
sbeps = 1.e-6;
System.out.println(maxel(vecsub(yout,yexp)));
localflag = maxel(vecsub(yout,yexp)) > sbeps;
globalflag = globalflag || localflag;
if (localflag) {
fail("*** rk4: Inaccurate Runge-Kutta step");
}
if (globalflag) System.out.println("Failed\n");
else System.out.println("Passed\n");
}
void rk4_derivs(final double x,final double[] y,final double[] dydx) {
dydx[0]= -y[1];
dydx[1]=y[0]-(1.0/x)*y[1];
dydx[2]=y[1]-(2.0/x)*y[2];
dydx[3]=y[2]-(3.0/x)*y[3];
}
class RK4_derivs implements DerivativeInf {
public void derivs(final double x, double[] y, double[] dydx){
rk4_derivs(x,y,dydx);
}
public void jacobian(final double x, double[] y, double[] dfdx, double[][] dfdy){}
}
}