Online PHP editor | refs for 5mPDp

<?php $array = array(); $meanax = 300; for($i = 0; $i < $meanax; $i++) { $array[$i] = rand(0, $meanax-1); } $s = sd($array); $mean = array_sum($array) / count($array); echo "\nbefore\n"; var_dump(array('s' => $s, 'm' => $mean)); $n = count($array); $x_new = 100000000; $x_quer_strich = m_reverse($n, $mean, $x_new); $s_new = sd_reverse($s, $n, $x_new, $x_quer_strich); echo "\nreverse\n"; var_dump(array('s' => $s_new, 'm' => $x_quer_strich)); $array[$n+1] = $x_new; $s = sd($array); $mean = array_sum($array) / count($array); echo "\nafter\n"; var_dump(array('s' => $s, 'm' => $mean)); echo "\nvalues array\n"; var_dump($array); // Function to calculate square of value - mean function sd_square($x, $mean) { return pow($x - $mean,2); } // Function to calculate standard deviation (uses sd_square) function sd($array) { // square root of sum of squares devided by N-1 return sqrt(array_sum(array_map("sd_square", $array, array_fill(0,count($array), (array_sum($array) / count($array)) ) ) ) / (count($array)-1) ); } function m_reverse($n, $mean, $x) { return ( $n * $mean + $x ) / ( $n + 1 ); } function sd_reverse($s, $n, $x, $mean) { return sqrt( 1 / $n * ( ( $n - 1 ) * pow( $s, 2 ) + ( $x - $mean ) ) ); }