Detailed explanation of PHP's method of calculating the stability of student scores

This article mainly introduces the stability operation of PHP to calculate student scores based on variance and standard deviation, and involves related operating skills of PHP mathematical operations. Friends in need can refer to it. I hope to be helpful.

The student side of the project has a personal growth profile module, which requires analyzing the student's performance stability through fluctuation collection based on the student's recent ten test scores. Anyone who has studied mathematics knows that this should be achieved using the variance in mathematics. Since I am a scumbag in mathematics, I had to read the relevant instructions and formulas online. See the picture below

Okay, now that you have the formula, it will be easy to do. Next It's just a formula.

$arr1 = array(50, 100, 100, 60, 50);
$arr2 = array(73, 70, 75, 72, 70);
function variance($arr) {
  $length = count($arr);
  if ($length == 0) {
    return array(0,0);
  }
  $average = array_sum($arr)/$length;
  $count = 0;
  foreach ($arr as $v) {
    $count += pow($average-$v, 2);
  }
  $variance = $count/$length;
  return array('variance' => $variance, 'square' => sqrt($variance), 'average' => $average);
}
print_r(variance($arr1));
print_r(variance($arr2));

The above code prints

Array
(
  [variance] => 536
  [square] => 23.15167380558
  [average] => 72
)
Array
(
  [variance] => 3.6
  [square] => 1.897366596101
  [average] => 72
)

By looking at the data, we found that although the average values ​​​​of the two arrays are the same, array 1 fluctuates greatly and the results are unstable, while array 2 fluctuates less and the results are lower than the array 1 stable.

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