/// Beta function. Beta(x,y)=Beta(y,x)=integral(0 to 1) {t^(x-1)*(1-t)^(y-1) dt}.
/// Also, Beta(x,y) = gamma(x)*gamma(y)/gamma(x+y).
/// @param x first argument
/// @param y second argument
/// @return beta(x,y)
/// @throw if either input argument is <= 0
double beta(const double& x, const double& y) throw(Exception)
{
try {
return ::exp(lnGamma(x) + lnGamma(y) - lnGamma(x+y));
}
catch(Exception& e) { GPSTK_RETHROW(e); }
}
/// Incomplete beta function I_x(a,b), 0<=x<=1, a,b>0
/// I sub x (a,b) = (1/beta(a,b)) integral (0 to x) { t^(a-1)*(1-t)^(b-1)dt }
/// @param double x input value, 0 <= x <= 1
/// @param double a input value, a > 0
/// @param double b input value, b > 0
/// @return Incomplete beta function I_x(a,b)
double incompleteBeta(const double& x, const double& a, const double& b)
throw(Exception)
{
if(x < 0 || x > 1) {
Exception e("Invalid x argument in incompleteBeta()");
GPSTK_THROW(e);
}
if(a <= 0 || b <= 0) {
Exception e("Non-positive argument in incompleteBeta()");
GPSTK_THROW(e);
}
if(x == 0) return 0.0;
if(x == 1) return 1.0;
try {
double factor = ::exp(lnGamma(a+b) - lnGamma(a) - lnGamma(b)
+ a * ::log(x) + b * ::log(1.0-x));
if(x < (a+1.0)/(a+b+2.0))
return factor*cfIBeta(x,a,b)/a;
else
return 1.0-factor*cfIBeta(1.0-x,b,a)/b;
}
catch(Exception& e) {
e.addText("Called by incompleteBeta()");
GPSTK_RETHROW(e);
}
}
/// Beta function. Beta(x,y)=Beta(y,x)=integral(0 to 1) {t^(x-1)*(1-t)^(y-1) dt}.
/// Also, Beta(x,y) = gamma(x)*gamma(y)/gamma(x+y).
/// @param double x first argument
/// @param double y second argument
/// @return beta(x,y)
/// @throw if either input argument is <= 0
double beta(const double& x, const double& y) throw(Exception)
{
try {
return ::exp(lnGamma(x) + lnGamma(y) - lnGamma(x+y));
}
catch(Exception& e) {
e.addText("Called by beta(x,y)");
GPSTK_RETHROW(e);
}
}
/// Gamma(x) the gamma function for positive argument.
/// Gamma(x) = integral(0 to inf) { t^(x-1) exp(-t) dt }
/// @param x argument, x must be > 0
/// @return double Gamma(x), the gamma function of x.
/// @throw if the input argument is <= 0
double Gamma(const double& x) throw(Exception)
{
try {
return ::exp(lnGamma(double(x)));
}
catch(Exception& e) { GPSTK_RETHROW(e); }
}
double lnFactorial(const int x) {
static const int maxTableSize = 128;
static double lut[maxTableSize]; // static arrays are automatically
// initialized with zero
if (x < 0) {
return NaN;
}
if (x <= 1) {
return 0.0;
}
if (x < maxTableSize) {
return (lut[static_cast<int>(x)] != 0) ? lut[static_cast<int>(x)] :
(lut[static_cast<int>(x)] = lnGamma(double(static_cast<int>(x)+1)));
}
return lnGamma(double(static_cast<int>(x)+1));
}
/// ln of Factorial of an integer, returned as a double.
/// @param n argument, n must be >= 0
/// @return ln(n!) or natural log of factorial(n), as a double
/// @throw if the input argument is < 0
double lnFactorial(const int& n) throw(Exception)
{
try {
if(n < 0) GPSTK_THROW(Exception("Negative argument"));
if(n <= 1) return 0.0;
return lnGamma(double(n+1));
}
catch(Exception& e) { GPSTK_RETHROW(e); }
}
/// ln of Factorial of an integer, returned as a double.
/// @param n int argument, n must be >= 0
/// @return ln(n!) or natural log of factorial(n), as a double
/// @throw if the input argument is < 0
double lnFactorial(const int& n) throw(Exception)
{
if(n < 0) {
Exception e("Negative argument in lnFactorial()");
GPSTK_THROW(e);
}
if(n <= 1) return 0.0;
return lnGamma(double(n+1));
}
double factorial(const int x) {
static const int maxLut = 34;
static const double lut[] = {1.0, // 0!
1.0, // 1!
2.0, // 2!
6.0, // 3!
24.0, // 4!
120.0, // 5!
720.0, // 6!
5040.0, // 7!
40320.0, // 8!
362880.0, // 9!
3628800.0, // 10!
39916800.0, // 11!
479001600.0, // 12!
6227020800.0, // 13!
87178291200.0, // 14!
1307674368000.0, // 15!
20922789888000.0, // 16!
355687428096000.0, // 17!
6402373705728000.0, // 18!
121645100408832000.0, // 19!
2432902008176640000.0, // 20!
51090942171709440000.0, // 21!
1124000727777607680000.0, // 22!
25852016738884976640000.0, // 23!
620448401733239439360000.0, // 24!
15511210043330985984000000.0, // 25!
403291461126605635584000000.0, // 26!
10888869450418352160768000000.0, // 27!
304888344611713860501504000000.0, // 28!
8841761993739701954543616000000.0, // 29!
265252859812191058636308480000000.0, // 30!
8222838654177922817725562880000000.0, // 31!
263130836933693530167218012160000000.0, // 32!
8683317618811886495518194401280000000.0 // 33!
};
if (x < 0) {
return NaN;
}
if (x>=maxLut) {
return exp(lnGamma(static_cast<double>(x+1)));
}
return lut[static_cast<int>(x)];
}
/// Factorial of an integer, returned as a double.
/// @param n int argument, n must be >= 0
/// @return n! or factorial(n), as a double
/// @throw if the input argument is < 0
double factorial(const int& n) throw(Exception)
{
if(n < 0) {
Exception e("Negative argument in factorial()");
GPSTK_THROW(e);
}
if(n > 32) return ::exp(lnGamma(double(n+1)));
static double store[33] = { 1.0, 1.0, 2.0, 6.0, 24.0, 120.0 };
static int nstore=5;
while(nstore < n) {
int i = nstore++;
store[nstore] = store[i] * nstore;
}
return store[n];
}
