double tgamma(double x) /* Gamma function */
{
int sign;
if (x == 0.0) { /* Pole Error */
errno = ERANGE;
return 1/x < 0 ? -HUGE_VAL : HUGE_VAL;
}
if (isinf(x)) {
if (x < 0) goto domain_error;
return x;
}
if (x < 0) {
static double zero = 0.0;
double i, f;
f = modf(-x, &i);
if (f == 0.0) { /* Domain Error */
domain_error:
errno = EDOM;
return zero/zero;
}
#ifndef HAVE_LGAMMA_R
sign = (fmod(i, 2.0) != 0.0) ? 1 : -1;
return sign * PI / (sin(PI * f) * exp(loggamma(1 - x)));
#endif
}
#ifndef HAVE_LGAMMA_R
return exp(loggamma(x));
#else
x = lgamma_r(x, &sign);
return sign * exp(x);
#endif
}
/*
Γ関数の値を求める
*/
double gamma(double x)
{
if (x < 0)
return M_PI / (sin(M_PI * x) * exp(loggamma(1 - x)));
else
return exp(loggamma(x));
}
/* the natural logarithm of the absolute value of the Gamma function */
double
lgamma_r(double x, int *signp)
{
if (x <= 0) {
double i, f, s;
f = modf(-x, &i);
if (f == 0.0) { /* pole error */
*signp = signbit(x) ? -1 : 1;
errno = ERANGE;
return HUGE_VAL;
}
*signp = (fmod(i, 2.0) != 0.0) ? 1 : -1;
s = sin(PI * f);
if (s < 0) s = -s;
return LOG_PI - log(s) - loggamma(1 - x);
}
*signp = 1;
return loggamma(x);
}
double CMultinomialTable::CalcLogZ( double *alpha , double *addData )
{
double sum = 0;
double z = 0;
for(int i=0 ; i<m_dim ; i++ )
{
if( addData )
{
sum += (alpha[i] + addData[i]);
z += loggamma( alpha[i] + addData[i] );
}
else
{
sum += alpha[i];
z += loggamma( alpha[i] );
}
}
z -= loggamma( sum );
return z;
}
