#include "matrix.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs,
                 const mxArray *prhs[])
{
   double *xp, *yp, *vp, *x0p, *y0p, *v0p, x0, y0;
   double vv;
   long i, N;
   x0p=mxGetPr(prhs[0]); y0p=mxGetPr(prhs[1]);
   v0p=mxGetPr(prhs[2]); N=mxGetM(prhs[2]); 
   plhs[0]=mxCreateDoubleMatrix(N,1, mxREAL);
   plhs[1]=mxCreateDoubleMatrix(N,1, mxREAL);
   xp=mxGetPr(plhs[0]); yp=mxGetPr(plhs[1]);
   xp[0]=x0p[0]; yp[0]=y0p[0];
   for (i=1; i<N; i++){
      vv=v0p[i];
      if (vv<0.05)
         {yp[i]=0.5*yp[i-1]; xp[i]=0;}
      else if (vv<0.45) {
         xp[i]=0.42*(xp[i-1]-yp[i-1]); yp[i]=0.2+0.42*(xp[i-1]+yp[i-1]);
      }
      else if (vv<0.85) {
         xp[i]=0.42*(xp[i-1]+yp[i-1]); yp[i]=0.2-0.42*(xp[i-1]-yp[i-1]);
      }
      else {xp[i]=0.1*xp[i-1]; yp[i]=0.1*yp[i-1]+0.2;}
   }
}