diff --git a/Classes/PHPExcel/Calculation/MathTrig.php b/Classes/PHPExcel/Calculation/MathTrig.php
index 346a5ff..35217b6 100644
--- a/Classes/PHPExcel/Calculation/MathTrig.php
+++ b/Classes/PHPExcel/Calculation/MathTrig.php
@@ -97,40 +97,58 @@ class PHPExcel_Calculation_MathTrig {
 	 * @param	float	$yCoordinate		The y-coordinate of the point.
 	 * @return	float	The inverse tangent of the specified x- and y-coordinates.
 	 */
-	public static function ATAN2($xCoordinate, $yCoordinate) {
-		$xCoordinate	= (float) PHPExcel_Calculation_Functions::flattenSingleValue($xCoordinate);
-		$yCoordinate	= (float) PHPExcel_Calculation_Functions::flattenSingleValue($yCoordinate);
+	public static function ATAN2($xCoordinate = NULL, $yCoordinate = NULL) {
+		$xCoordinate	= PHPExcel_Calculation_Functions::flattenSingleValue($xCoordinate);
+		$yCoordinate	= PHPExcel_Calculation_Functions::flattenSingleValue($yCoordinate);
 
-		if (($xCoordinate == 0) && ($yCoordinate == 0)) {
-			return PHPExcel_Calculation_Functions::DIV0();
+		$xCoordinate	= ($xCoordinate !== NULL)	? $xCoordinate : 0.0;
+		$yCoordinate	= ($yCoordinate !== NULL)	? $yCoordinate : 0.0;
+
+		if (((is_numeric($xCoordinate)) || (is_bool($xCoordinate))) &&
+			((is_numeric($yCoordinate)))  || (is_bool($yCoordinate))) {
+			$xCoordinate	= (float) $xCoordinate;
+			$yCoordinate	= (float) $yCoordinate;
+
+			if (($xCoordinate == 0) && ($yCoordinate == 0)) {
+				return PHPExcel_Calculation_Functions::DIV0();
+			}
+
+			return atan2($yCoordinate, $xCoordinate);
 		}
-
-		return atan2($yCoordinate, $xCoordinate);
-	}	//	function REVERSE_ATAN2()
+		return PHPExcel_Calculation_Functions::VALUE();
+	}	//	function ATAN2()
 
 
 	/**
 	 * CEILING
 	 *
 	 * Returns number rounded up, away from zero, to the nearest multiple of significance.
+	 *		For example, if you want to avoid using pennies in your prices and your product is
+	 *		priced at $4.42, use the formula =CEILING(4.42,0.05) to round prices up to the
+	 *		nearest nickel.
 	 *
-	 * @param	float	$number			Number to round
-	 * @param	float	$significance	Significance
+	 * Excel Function:
+	 *		CEILING(number[,significance])
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
+	 * @param	float	$number			The number you want to round.
+	 * @param	float	$significance	The multiple to which you want to round.
 	 * @return	float	Rounded Number
 	 */
-	public static function CEILING($number,$significance=null) {
+	public static function CEILING($number, $significance = NULL) {
 		$number			= PHPExcel_Calculation_Functions::flattenSingleValue($number);
 		$significance	= PHPExcel_Calculation_Functions::flattenSingleValue($significance);
 
-		if ((is_null($significance)) && (PHPExcel_Calculation_Functions::getCompatibilityMode() == PHPExcel_Calculation_Functions::COMPATIBILITY_GNUMERIC)) {
+		if ((is_null($significance)) &&
+			(PHPExcel_Calculation_Functions::getCompatibilityMode() == PHPExcel_Calculation_Functions::COMPATIBILITY_GNUMERIC)) {
 			$significance = $number/abs($number);
 		}
 
 		if ((is_numeric($number)) && (is_numeric($significance))) {
-			if (self::SIGN($number) == self::SIGN($significance)) {
-				if ($significance == 0.0) {
-					return 0;
-				}
+			if ($significance == 0.0) {
+				return 0.0;
+			} elseif (self::SIGN($number) == self::SIGN($significance)) {
 				return ceil($number / $significance) * $significance;
 			} else {
 				return PHPExcel_Calculation_Functions::NaN();
@@ -146,11 +164,16 @@ class PHPExcel_Calculation_MathTrig {
 	 * Returns the number of combinations for a given number of items. Use COMBIN to
 	 *		determine the total possible number of groups for a given number of items.
 	 *
+	 * Excel Function:
+	 *		COMBIN(numObjs,numInSet)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	int		$numObjs	Number of different objects
 	 * @param	int		$numInSet	Number of objects in each combination
 	 * @return	int		Number of combinations
 	 */
-	public static function COMBIN($numObjs,$numInSet) {
+	public static function COMBIN($numObjs, $numInSet) {
 		$numObjs	= PHPExcel_Calculation_Functions::flattenSingleValue($numObjs);
 		$numInSet	= PHPExcel_Calculation_Functions::flattenSingleValue($numInSet);
 
@@ -170,7 +193,16 @@ class PHPExcel_Calculation_MathTrig {
 	 * EVEN
 	 *
 	 * Returns number rounded up to the nearest even integer.
+	 * You can use this function for processing items that come in twos. For example,
+	 *		a packing crate accepts rows of one or two items. The crate is full when
+	 *		the number of items, rounded up to the nearest two, matches the crate's
+	 *		capacity.
 	 *
+	 * Excel Function:
+	 *		EVEN(number)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	float	$number			Number to round
 	 * @return	int		Rounded Number
 	 */
@@ -195,7 +227,13 @@ class PHPExcel_Calculation_MathTrig {
 	 * FACT
 	 *
 	 * Returns the factorial of a number.
+	 * The factorial of a number is equal to 1*2*3*...* number.
 	 *
+	 * Excel Function:
+	 *		FACT(factVal)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	float	$factVal	Factorial Value
 	 * @return	int		Factorial
 	 */
@@ -228,6 +266,11 @@ class PHPExcel_Calculation_MathTrig {
 	 *
 	 * Returns the double factorial of a number.
 	 *
+	 * Excel Function:
+	 *		FACTDOUBLE(factVal)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	float	$factVal	Factorial Value
 	 * @return	int		Double Factorial
 	 */
@@ -255,11 +298,16 @@ class PHPExcel_Calculation_MathTrig {
 	 *
 	 * Rounds number down, toward zero, to the nearest multiple of significance.
 	 *
+	 * Excel Function:
+	 *		FLOOR(number[,significance])
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	float	$number			Number to round
 	 * @param	float	$significance	Significance
 	 * @return	float	Rounded Number
 	 */
-	public static function FLOOR($number,$significance=null) {
+	public static function FLOOR($number, $significance = NULL) {
 		$number			= PHPExcel_Calculation_Functions::flattenSingleValue($number);
 		$significance	= PHPExcel_Calculation_Functions::flattenSingleValue($significance);
 
@@ -284,20 +332,27 @@ class PHPExcel_Calculation_MathTrig {
 	/**
 	 * GCD
 	 *
-	 * Returns the greatest common divisor of a series of numbers
+	 * Returns the greatest common divisor of a series of numbers.
+	 * The greatest common divisor is the largest integer that divides both
+	 *		number1 and number2 without a remainder.
 	 *
-	 * @param	$array	Values to calculate the Greatest Common Divisor
-	 * @return	int		Greatest Common Divisor
+	 * Excel Function:
+	 *		GCD(number1[,number2[, ...]])
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
+	 * @param	mixed	$arg,...		Data values
+	 * @return	integer					Greatest Common Divisor
 	 */
 	public static function GCD() {
 		$returnValue = 1;
-		$allPoweredFactors = array();
+		$allValuesFactors = array();
 		// Loop through arguments
 		foreach(PHPExcel_Calculation_Functions::flattenArray(func_get_args()) as $value) {
 			if (!is_numeric($value)) {
 				return PHPExcel_Calculation_Functions::VALUE();
 			} elseif ($value == 0) {
-				break;
+				continue;
 			} elseif($value < 0) {
 				return PHPExcel_Calculation_Functions::NaN();
 			}
@@ -306,6 +361,10 @@ class PHPExcel_Calculation_MathTrig {
 			$allValuesFactors[] = $myCountedFactors;
 		}
 		$allValuesCount = count($allValuesFactors);
+		if ($allValuesCount == 0) {
+			return 0;
+		}
+
 		$mergedArray = $allValuesFactors[0];
 		for ($i=1;$i < $allValuesCount; ++$i) {
 			$mergedArray = array_intersect_key($mergedArray,$allValuesFactors[$i]);
@@ -351,6 +410,11 @@ class PHPExcel_Calculation_MathTrig {
 	 *
 	 * Casts a floating point value to an integer
 	 *
+	 * Excel Function:
+	 *		INT(number)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	float	$number			Number to cast to an integer
 	 * @return	integer	Integer value
 	 */
@@ -373,8 +437,16 @@ class PHPExcel_Calculation_MathTrig {
 	 * LCM
 	 *
 	 * Returns the lowest common multiplier of a series of numbers
+	 * The least common multiple is the smallest positive integer that is a multiple
+	 * of all integer arguments number1, number2, and so on. Use LCM to add fractions
+	 * with different denominators.
 	 *
-	 * @param	$array	Values to calculate the Lowest Common Multiplier
+	 * Excel Function:
+	 *		LCM(number1[,number2[, ...]])
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
+	 * @param	mixed	$arg,...		Data values
 	 * @return	int		Lowest Common Multiplier
 	 */
 	public static function LCM() {
@@ -427,7 +499,7 @@ class PHPExcel_Calculation_MathTrig {
 	 * @param	float	$base		The base of the logarithm. If base is omitted, it is assumed to be 10.
 	 * @return	float
 	 */
-	public static function LOG_BASE($number = NULL, $base=10) {
+	public static function LOG_BASE($number = NULL, $base = 10) {
 		$number	= PHPExcel_Calculation_Functions::flattenSingleValue($number);
 		$base	= (is_null($base))	? 10 :	(float) PHPExcel_Calculation_Functions::flattenSingleValue($base);
 
@@ -442,6 +514,13 @@ class PHPExcel_Calculation_MathTrig {
 	/**
 	 * MDETERM
 	 *
+	 * Returns the matrix determinant of an array.
+	 *
+	 * Excel Function:
+	 *		MDETERM(array)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	array	$matrixValues	A matrix of values
 	 * @return	float
 	 */
@@ -476,6 +555,13 @@ class PHPExcel_Calculation_MathTrig {
 	/**
 	 * MINVERSE
 	 *
+	 * Returns the inverse matrix for the matrix stored in an array.
+	 *
+	 * Excel Function:
+	 *		MINVERSE(array)
+	 *
+	 * @access	public
+	 * @category Mathematical and Trigonometric Functions
 	 * @param	array	$matrixValues	A matrix of values
 	 * @return	array
 	 */