Data commit

Task/Arithmetic-geometric-mean/PHP/arithmetic-geometric-mean.php

@@ -0,0 +1,22 @@
+define('PRECISION', 13);
+
+function agm($a0, $g0, $tolerance = 1e-10)
+{
+    // the bc extension deals in strings and cannot convert
+    // floats in scientific notation by itself - hence
+    // this manual conversion to a string
+    $limit = number_format($tolerance, PRECISION, '.', '');
+    $an    = $a0;
+    $gn    = $g0;
+    do {
+        list($an, $gn) = array(
+            bcdiv(bcadd($an, $gn), 2),
+            bcsqrt(bcmul($an, $gn)),
+        );
+    } while (bccomp(bcsub($an, $gn), $limit) > 0);
+
+    return $an;
+}
+
+bcscale(PRECISION);
+echo agm(1, 1 / bcsqrt(2));