Merge pull request #49 from codisart/add-arcsec-arccsc-methods

[TECH] Add two new methods and their tests. Thanks to @codisart .

Author: castarco

src/Decimal.php

@@ -908,6 +908,68 @@ public function arccot($scale = null) {
         )->round($scale);
     }
 
+    /**
+     * Calculates the arcsecant of this with the highest possible accuracy
+     *
+     * @param integer $scale
+     * @return Decimal
+     */
+    public function arcsec($scale = null) {
+        if($this->comp(DecimalConstants::one(), $scale + 2) === -1 && $this->comp(DecimalConstants::negativeOne(), $scale + 2) === 1) {
+            throw new \DomainException(
+                "The arcsecant of this number is undefined."
+            );
+        }
+
+        $piOverTwo = DecimalConstants::pi()->div(Decimal::fromInteger(2), $scale + 2)->round($scale);
+
+        if ($this->round($scale)->equals(DecimalConstants::one())) {
+            return DecimalConstants::zero();
+        }
+        if ($this->round($scale)->equals(DecimalConstants::negativeOne())) {
+            return DecimalConstants::pi()->round($scale);
+        }
+
+        $scale = ($scale === null) ? 32 : $scale;
+
+        return $piOverTwo->sub(
+            self::powerSerie(
+                DecimalConstants::one()->div($this, $scale + 2),
+                DecimalConstants::zero(),
+                $scale + 2
+            )
+        )->round($scale);
+    }
+
+    /**
+     * Calculates the arccosecant of this with the highest possible accuracy
+     *
+     * @param integer $scale
+     * @return Decimal
+     */
+    public function arccsc($scale = null) {
+        if($this->comp(DecimalConstants::one(), $scale + 2) === -1 && $this->comp(DecimalConstants::negativeOne(), $scale + 2) === 1) {
+            throw new \DomainException(
+                "The arccosecant of this number is undefined."
+            );
+        }
+
+        $scale = ($scale === null) ? 32 : $scale;
+
+        if ($this->round($scale)->equals(DecimalConstants::one())) {
+            return DecimalConstants::pi()->div(Decimal::fromInteger(2), $scale + 2)->round($scale);
+        }
+        if ($this->round($scale)->equals(DecimalConstants::negativeOne())) {
+            return DecimalConstants::pi()->div(Decimal::fromInteger(-2), $scale + 2)->round($scale);
+        }
+
+        return self::powerSerie(
+            DecimalConstants::one()->div($this, $scale + 2),
+            DecimalConstants::zero(),
+            $scale + 2
+        )->round($scale);
+    }
+
     /**
      * Returns exp($this), said in other words: e^$this .
      *

tests/Decimal/DecimalArccscTest.php

@@ -0,0 +1,42 @@
+<?php
+
+use Litipk\BigNumbers\Decimal as Decimal;
+
+/**
+ * @group arccsc
+ */
+class DecimalArccscTest extends PHPUnit_Framework_TestCase
+{
+    public function arccscProvider() {
+        // Some values provided by wolframalpha
+        return [
+            ['25.546', '0.03915507577327', 14],
+            ['1.5', '0.729728', 6],
+            ['1', '1.57079632679489662', 17],
+            ['-1', '-1.57079632679489662', 17],
+        ];
+    }
+
+    /**
+     * @dataProvider arccscProvider
+     */
+    public function testSimple($nr, $answer, $digits)
+    {
+        $x = Decimal::fromString($nr);
+        $arccscX = $x->arccsc($digits);
+
+        $this->assertTrue(
+            Decimal::fromString($answer)->equals($arccscX),
+            "The answer must be " . $answer . ", but was " . $arccscX
+        );
+    }
+
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage The arccosecant of this number is undefined.
+     */
+    public function testArccscBetweenOneAndNegativeOne()
+    {
+        Decimal::fromString('0.546')->arccsc();
+    }
+}

tests/Decimal/DecimalArcsecTest.php

@@ -0,0 +1,42 @@
+<?php
+
+use Litipk\BigNumbers\Decimal as Decimal;
+
+/**
+ * @group arcsec
+ */
+class DecimalArcsecTest extends PHPUnit_Framework_TestCase
+{
+    public function arcsecProvider() {
+        // Some values provided by wolframalpha
+        return [
+            ['25.546', '1.53164125102163', 14],
+            ['1.5', '0.841068', 6],
+            ['1', '0', 17],
+            ['-1', '3.14159265358979324', 17],
+        ];
+    }
+
+    /**
+     * @dataProvider arcsecProvider
+     */
+    public function testSimple($nr, $answer, $digits)
+    {
+        $x = Decimal::fromString($nr);
+        $arcsecX = $x->arcsec($digits);
+
+        $this->assertTrue(
+            Decimal::fromString($answer)->equals($arcsecX),
+            "The answer must be " . $answer . ", but was " . $arcsecX
+        );
+    }
+
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage The arcsecant of this number is undefined.
+     */
+    public function testArcsecBetweenOneAndNegativeOne()
+    {
+        Decimal::fromString('0.546')->arcsec();
+    }
+}