[TECH] Add the cosec method for the Decimal class and the test.

Author: codisart

src/Decimal.php

@@ -713,6 +713,25 @@ function ($i) {
         );
     }
 
+    /**
+     * Calculates the cosecant of this with the highest possible accuracy
+     * Note that accuracy is limited by the accuracy of predefined PI;
+     *
+     * @param integer $scale
+     * @return Decimal
+     */
+    public function cosec($scale = null)
+    {
+        $sin = $this->sin($scale + 2);
+        if ($sin->isZero()) {
+            throw new \DomainException(
+                "The cosecant of this 'angle' is undefined."
+            );
+        }
+
+        return Decimal::fromInteger(1)->div($sin)->round($scale);
+    }
+
     /**
      * Calculates the cosine of this method with the highest possible accuracy
      * Note that accuracy is limited by the accuracy of predefined PI;

tests/Decimal/DecimalCosecTest.php

@@ -0,0 +1,32 @@
+<?php
+
+use Litipk\BigNumbers\Decimal as Decimal;
+
+/**
+ * @group cosec
+ */
+class DecimalCosecTest extends PHPUnit_Framework_TestCase
+{
+    public function cosecProvider() {
+        // Some values provided by Mathematica
+        return [
+            ['1', '1.18839510577812', 14],
+            ['123.123', '-1.76874094322450309', 17],
+            ['15000000000', '1.44570405082842149818', 20]
+        ];
+    }
+
+    /**
+     * @dataProvider cosecProvider
+     */
+    public function testSimple($nr, $answer, $digits)
+    {
+        $x = Decimal::fromString($nr);
+        $cosecX = $x->cosec((int)$digits);
+
+        $this->assertTrue(
+            Decimal::fromString($answer)->equals($cosecX),
+            "The answer must be " . $answer . ", but was " . $cosecX
+        );
+    }
+}