Merge pull request #25 from punkka/cotan-add

Adding the method cotan for the calculus of the cotangente, by @punkka .

Author: castarco

src/Decimal.php

@@ -777,6 +777,24 @@ 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.
      *

src/InfiniteDecimal.php

@@ -321,6 +321,14 @@ public function tan($scale = null)
         );
     }
 
+    public function cotan($scale = null)
+    {
+        throw new \DomainException(($this === self::$pInf) ?
+            "Cotangent function hasn't limit in the positive infinite." :
+            "Cotangent function hasn't limit in the negative infinite."
+        );
+    }
+
     /**
      * @param  integer $scale Has no effect, exists only for compatibility.
      * @return boolean

tests/Decimal/DecimalCotanTest.php

@@ -0,0 +1,44 @@
+<?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
+        );
+    }
+    
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage The cotangent of this 'angle' is undefined.
+     */
+    public function testCotanPiDiv()
+    {    	
+        $PI  = DecimalConstants::PI();
+        $PI->cotan();
+    }
+    
+}

tests/Decimal/DecimalTanTest.php

@@ -1,6 +1,6 @@
 <?php
 
-use Litipk\BigNumbers\Decimal as Decimal;
+use \Litipk\BigNumbers\Decimal as Decimal;
 use \Litipk\BigNumbers\DecimalConstants as DecimalConstants;
 
 /**
@@ -39,4 +39,5 @@ public function testTanPiTwoDiv()
         $PiDividedByTwo = DecimalConstants::PI()->div(Decimal::fromInteger(2));
         $PiDividedByTwo->tan();
     }
+
 }

tests/InfiniteDecimal/InfiniteDecimalCotanTest.php

@@ -0,0 +1,27 @@
+<?php
+
+use Litipk\BigNumbers\InfiniteDecimal as InfiniteDecimal;
+
+/**
+ * @group cotan
+ */
+class InfiniteDecimalCotanTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage Cotangent function hasn't limit in the positive infinite.
+     */
+    public function testFinitePositiveInfiniteCotan()
+    {
+        InfiniteDecimal::getPositiveInfinite()->cotan();
+    }
+
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage Cotangent function hasn't limit in the negative infinite.
+     */
+    public function testFiniteNegativeInfiniteCotan()
+    {
+        InfiniteDecimal::getNegativeInfinite()->cotan();
+    }
+}