private static double[] copyOf(final double[] values,final int begin,final int length){
  MathArrays.verifyValues(values,begin,length);
  return Arrays.copyOfRange(values,begin,begin + length);
}

private static double [ ] copyOf ( final double [ ] values , final int begin , final int length ) { MathArrays . verifyValues ( values , begin , length ) ; return Arrays . copyOfRange ( values , begin , begin + length ) ; }
make a copy of the array for the slice defined by array part from [ begin , begin + length )
