int inverse(Block vb, Object vl, float[][] in, int[] nonzero, int ch){
    int i=0;
    for(i=0; i<ch; i++)
      if(nonzero[i]!=0)
        break;
    if(i==ch)
      return (0); /* no nonzero vectors */

    return (_2inverse(vb, vl, in, ch));
  }