# 余弦(近似) Cosine Approximation
# 引数 値 ($x)
# 戻り値 余弦(ラジアン) ($CosineApproximation)
sub COSINE{
	my ($x) = @_;
	my $CosineApproximation = 0;
	my $Cosine = 0;
	my $PrevCosine = 0;
	my $X = 0;
	my $Sign = 0;
	my $Num = 0;
	my $Factorial = 1;
	my $Pi = atan2(1, 1) * 4;
	my $Radian2Pi = 2 * $Pi;
	my $Limit = 100;
	my $Epsilon = 1.0e-20;
	
	# $Radian2Pi = 360度
	if((-$Radian2Pi < $x) && ($x < $Radian2Pi)){
		$X = $x;
	}else {
		$X = $x - (int($x / $Radian2Pi) * $Radian2Pi);
	}
	
	for(my $i = 0; $i < $Limit; $i++){
		# 符号
		$Sign = (($i % 2) == 0 ? 1: -1);
		# 分子
		$Num = $X ** (2 * $i);
	
		if($i != 0){
	
			# 分母 階乗
			for(my $j = 2 * $i; $j > (2 * ($i - 1)); $j--){
				$Factorial = $Factorial * $j;
			}
		}
	
		# 一つ前
		$PrevCosine = $Cosine;
		# 余弦(近似) Cosine
		$Cosine += $Sign * ($Num / $Factorial);
	
		# 収束判定
		last if(abs($Cosine - $PrevCosine) < $Epsilon);
	}
	
	# 余弦(近似) Cosine
	$CosineApproximation = $Cosine;
	
	return $CosineApproximation;
}