Unexpected T_STRING error (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?

You don't need brackets in this expression (and others): (($n * $xx_sum) – ($x_sum * $x_sum));. PHP's operator precedence follows arithmetic conventions. — hek2mgl
– hek2mgl, Commented Nov 10, 2013 at 3:07
The error persists even if you take off the outer set of parenthesis. — gtilflm
– gtilflm, Commented Nov 10, 2013 at 3:08
okay so I copied this over and ran it and got the error. I was shocked. And then I slowly started to add/remove variables and I don't know why that happened but it works now? Same whitespace and brackets and everything. I just replaced the variables with 1 and added/removed things. I have no idea why it happened or what I fixed. — gloomy.penguin
– gloomy.penguin, Commented Nov 10, 2013 at 3:11
Is the minus sign actually a minus sign. I've had situations where I was copy/pasting and the minus symbol was an html entity an not the actual symbol. — user2417483
– user2417483, Commented Nov 10, 2013 at 3:11
This question appears to be off-topic because it is about a syntax error. — mario
– mario, Commented Nov 10, 2013 at 3:14

Adam D. Ruppe · Accepted Answer · 2013-11-10 03:13:13Z

2

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

answered Nov 10, 2013 at 3:13

Adam D. Ruppe

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2 Comments

Adam D. Ruppe Over a year ago

The way I found it btw was just copy/pasting the code from firefox into an rxvt to run it on the php command line. rxvt pasted it as \uxxxx instead of -, triggering a warning and error from php and immediately looking different too.

gtilflm Over a year ago

@JakeGould: Actually it was "Jeff" in the comments. Beat Adam by a nose.

Wagner Leonardi · Accepted Answer · 2013-11-10 03:15:37Z

1

Don't ask me how I discovered that, but your "-" is not a real "-", is another character, but have the same apparence

Ok you didn't asked me, but I have discovered at http://writecodeonline.com/php/ , it doesn't recognize yours "-" character

Now working code with real "-", you can copy an paste, and see:

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)) );

answered Nov 10, 2013 at 3:15

Wagner Leonardi

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2 Comments

gloomy.penguin Over a year ago

how did that happen?? i was shocked when i copied and pasted the code and the error was real... lol... how do you think he got a - that was fake?

Wagner Leonardi Over a year ago

I don't have php at my pc so I used writecodeonline.com/php and it recognized that "-" was actually another character per encoding. Was pretty easy.

user1864610 · Accepted Answer · 2013-11-10 03:14:25Z

0

I retyped the offending line like this:

$divisor = (($n*$xx_sum)-($x_sum * $x_sum));

The error disappeared. After a bit of poking the error seems to be related to the minus sign in the middle. deleting it and retyping it seems to fix the problem.

See this fiddle:

answered Nov 10, 2013 at 3:14

user1864610

Comments

Giacomo1968 · Accepted Answer · 2013-11-10 03:14:35Z

Adam is right, but also, you didn’t close the for loop. Here try this.

Also, the minus sign was the wrong sign here:

$divisor = (($n * $xx_sum) - ($x_sum * $x_sum));

As well as here:

$m = (($n * $xy_sum) - ($x_sum * $y_sum)) / $divisor;

My cleaned up version of your function with the closed for loop in place as well here.

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);

} // linear_regression

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