Data commit

Task/Gaussian-elimination/PHP/gaussian-elimination.php

@@ -0,0 +1,75 @@
+function swap_rows(&$a, &$b, $r1, $r2)
+{
+    if ($r1 == $r2) return;
+
+    $tmp = $a[$r1];
+    $a[$r1] = $a[$r2];
+    $a[$r2] = $tmp;
+
+    $tmp = $b[$r1];
+    $b[$r1] = $b[$r2];
+    $b[$r2] = $tmp;
+}
+
+function gauss_eliminate($A, $b, $N)
+{
+    for ($col = 0; $col < $N; $col++)
+    {
+        $j = $col;
+        $max = $A[$j][$j];
+
+        for ($i = $col + 1; $i < $N; $i++)
+        {
+            $tmp = abs($A[$i][$col]);
+            if ($tmp > $max)
+            {
+                $j = $i;
+                $max = $tmp;
+            }
+        }
+
+        swap_rows($A, $b, $col, $j);
+
+        for ($i = $col + 1; $i < $N; $i++)
+        {
+            $tmp = $A[$i][$col] / $A[$col][$col];
+            for ($j = $col + 1; $j < $N; $j++)
+            {
+                $A[$i][$j] -= $tmp * $A[$col][$j];
+            }
+            $A[$i][$col] = 0;
+            $b[$i] -= $tmp * $b[$col];
+        }
+    }
+    $x = array();
+    for ($col = $N - 1; $col >= 0; $col--)
+    {
+        $tmp = $b[$col];
+        for ($j = $N - 1; $j > $col; $j--)
+        {
+            $tmp -= $x[$j] * $A[$col][$j];
+        }
+        $x[$col] = $tmp / $A[$col][$col];
+    }
+    return $x;
+}
+
+function test_gauss()
+{
+    $a = array(
+        array(1.00, 0.00, 0.00,  0.00,  0.00, 0.00),
+        array(1.00, 0.63, 0.39,  0.25,  0.16, 0.10),
+        array(1.00, 1.26, 1.58,  1.98,  2.49, 3.13),
+        array(1.00, 1.88, 3.55,  6.70, 12.62, 23.80),
+        array(1.00, 2.51, 6.32, 15.88, 39.90, 100.28),
+        array(1.00, 3.14, 9.87, 31.01, 97.41, 306.02)
+    );
+    $b = array( -0.01, 0.61, 0.91, 0.99, 0.60, 0.02 );
+
+    $x = gauss_eliminate($a, $b, 6);
+
+    ksort($x);
+    print_r($x);
+}
+
+test_gauss();