abstract class fij_xi extends Mathd
{
  // multifunction multi independent variable
  // vector of dependent variables are returned
  // example f[0][0]=x[0]+sin(x[1])  f[0][1]=x[0]*x[1]
  //         f[1][0]=x[0]*x[0]-x[1]  f[1][1]=x[0]+x[1]*x[0]
  // func(x) returns the value of f[0][0] and f[0][1]
  //                              f[0][1] and f[1][1]
  // as a two dimensional vector
  //
  abstract double[][] func(double x[]);
}
