意外的T_STRING错误（PHP）

Question

I can normally catch these easy, but......

function linear_regression($x, $y) {

// calculate number points
$n = count($x);

// ensure both arrays of points are the same size
if ($n != count($y)) {

trigger_error("linear_regression(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);

}

// calculate sums
$x_sum = array_sum($x);
$y_sum = array_sum($y);

$xx_sum = 0;
$xy_sum = 0;

for($i = 0; $i < $n; $i++) {

$xy_sum+=($x[$i]*$y[$i]);
$xx_sum+=($x[$i]*$x[$i]);

  }



  // calculate slope
  //$m = (($n * $xy_sum) - ($x_sum * $y_sum)) / (($n * $xx_sum) - ($x_sum * $x_sum));

  $divisor = (($n * $xx_sum) – ($x_sum * $x_sum));
if ($divisor == 0){
 $m = 0;
} else {
$m = (($n * $xy_sum) – ($x_sum * $y_sum)) / $divisor;
}


  // calculate intercept
  $b = ($y_sum - ($m * $x_sum)) / $n;

  // return result
  return array("m"=>$m, "b"=>$b);

}

var_dump( linear_regression(array(1, 2, 3, 4, 4), array(1.5, 1.6, 2.1, 3.0, 6)) );

The error is happening here $divisor = (($n * $xx_sum) – ($x_sum * $x_sum));

Any ideas why?

Answer 1

The minus sign is a fancy unicode dash (I think the em dash) instead of the regular ascii - character.