code: function signum( y, x ) {
  	var len = x.length,
  		i;
  	if ( y.length !== len ) {
  		throw new Error( 'signum()::invalid input arguments. Input and output matrices must be the same length.' );
  	}
  	for ( i = 0; i < len; i++ ) {
  		y.data[ i ] = SIGN( x.data[ i ] );
  	}
  	return y;
  }
docs: SIGNUM FUNCTION // 
  FUNCTION: signum( out, matrix )
  Evaluates the signum function for each matrix element.
  
  @param {Matrix} out - output matirx
  @param {Matrix} arr - input matrix
  @returns {Matrix} output matrix