// test_math_64.java  test dot and cross product of two vectors

public class test_math_64
{
  public test_math_64()
  {
    int n = 4;
    double x[] = {2.0,  3.0, 4.0, 5.0};
    double y[] = {5.0, -3.0, 2.0, 4.0};
    double z[] = {-1.0, -1.0, -1.0, 1.0}; // initial junk
    double sum;

    System.out.println("test_math_64.c running n = "+n);
    System.out.println("x = "+x[0]+", "+x[1]+", "+x[2]+", "+x[3]);
    System.out.println("y = "+y[0]+", "+y[1]+", "+y[2]+", "+y[3]);
    sum = dot(x, y);
    System.out.println("dot(n, x, y) = "+sum);
    System.out.println(" ");
    System.out.println("x = "+x[0]+", "+x[1]+", "+x[2]+", "+x[3]);
    System.out.println("y = "+y[0]+", "+y[1]+", "+y[2]+", "+y[3]);
    cross(x, y, z);
    System.out.println("x cross y = z = "+z[0]+", "+z[1]+", "+z[2]+", "+z[3]);
  } // end test_math_64

  public double dot(double x[], double y[])
  {
    double sum = 0.0;
    int n = x.length;

    for(int i=0; i<n; i++) sum = sum + x[i]*y[i];
    return sum;
  } // end dot

  public void cross(double x[], double y[], double z[])
  {
    double sign = 1.0;
    int n = x.length;
    int k;
    for(int m=0; m<n; m++) // answer
    {
      z[m] = 0.0;
      for(int j=0; j<n; j++) // column
      {
        k = j+m;
        if(k>=n) k = k-n;
        z[m] = z[m] + x[j]*y[k];
      } // end j
      z[m] = sign*z[m];
      sign = -sign;
    } // end m
  } // end cross

  public static void main (String[] args)
  {
    new test_math_64();
  }
} // end test_math_64.java