Adding the method cotan for the calculus of the cotangente

Author: codisart

src/Decimal.php

@@ -753,6 +753,24 @@ public function tan($scale = null) {
 	    return $this->sin($scale + 2)->div($cos)->round($scale);
     }
 
+    /**
+     * Calculates the cotangent of this method with the highest possible accuracy
+     * Note that accuracy is limited by the accuracy of predefined PI;
+     *
+     * @param integer $scale
+     * @return Decimal cotan($this)
+     */
+    public function cotan($scale = null) {
+	    $sin = $this->sin($scale + 2);
+	    if ($sin->isZero()) {
+	        throw new \DomainException(
+	            "The cotangent of this 'angle' is undefined."
+	        );
+	    }
+
+	    return $this->cos($scale + 2)->div($sin)->round($scale);
+    }
+
     /**
      * Indicates if the passed parameter has the same sign as the method's bound object.
      *

tests/Decimal/DecimalCotanTest.php

@@ -0,0 +1,47 @@
+<?php
+
+use \Litipk\BigNumbers\Decimal as Decimal;
+use \Litipk\BigNumbers\DecimalConstants as DecimalConstants;
+
+/**
+ * @group cotan
+ */
+class DecimalCotanTest extends PHPUnit_Framework_TestCase
+{
+    public function cotanProvider() {
+        // Some values providede by mathematica
+        return array(
+            array('1', '0.64209261593433', 14),
+            array('123.123', '1.45891895739232371', 17),
+            array('15000000000', '-1.04405948230055701685', 20)
+
+        );
+    }
+
+    /**
+     * @dataProvider cotanProvider
+     */
+    public function testSimple($nr, $answer, $digits)
+    {
+        $x = Decimal::fromString($nr);
+        $cotanX = $x->cotan($digits);
+        $this->assertTrue(
+            Decimal::fromString($answer)->equals($cotanX),
+            'cotan('.$nr.') must be equal to '.$answer.', but was '.$cotanX
+        );
+    }
+    
+    public function testCotanPiDiv()
+    {    	
+        $PI  = DecimalConstants::PI();
+
+        $catched = false;
+        try {
+            $PI->cotan();
+        } catch (\DomainException $e) {
+            $catched = true;
+        }
+        $this->assertTrue($catched);
+    }
+    
+}