static int cdf_dpois (lua_State *L) {
/* stack should contain s and xlam */
lua_Number s = luaL_checknumber(L, 1);
lua_Number xlam = luaL_checknumber(L, 2);
lua_Number d;
check_pois(L, 1, s, xlam);
d = s+1;
d = exp(s*log(xlam)-xlam-dlngam(&d));
lua_pushnumber(L, d);
return 1;
}
/* scale here is 1/rate */
static int cdf_dgamma (lua_State *L) {
/* stack should contain x, shape and opt. scale */
lua_Number x = luaL_checknumber(L, 1);
lua_Number shape = luaL_checknumber(L, 2);
lua_Number scale = luaL_optnumber(L, 3, 1);
lua_Number d;
check_gamma(L, 1, x, shape, scale);
d = x * scale;
d = exp(shape*log(d)-d-dlngam(&shape))/x;
lua_pushnumber(L, d);
return 1;
}
static int cdf_dchisq (lua_State *L) {
/* stack should contain x, df and opt. pnonc */
lua_Number x = luaL_checknumber(L, 1);
lua_Number df = luaL_checknumber(L, 2);
lua_Number pnonc = 0;
lua_Number d;
check_chisq(L, 1, x, df, pnonc);
/* compute central dchisq */
d = df/2;
d = exp((d-1)*log(x)-x/2-d*M_LN2-dlngam(&d));
lua_pushnumber(L, d);
return 1;
}
static int stat_dchisq (lua_State *L) {
/* stack should contain x, df and opt. pnonc */
lua_Number x = luaL_checknumber(L, 1);
lua_Number df = luaL_checknumber(L, 2);
lua_Number pnonc = luaL_optnumber(L, 3, 0);
lua_Number d;
check_chisq(L, 1, x, df, pnonc);
/* compute central dchisq */
d = df / 2;
d = exp((d - 1) * log(x) - x / 2 - d * M_LN2 - dlngam(&d));
/* compute non-central if that's the case */
if (pnonc != 0) { /* non-central? */
/* evaluate weighted series */
int i;
lua_Number t = d *= exp(-pnonc / 2); /* first term */
for (i = 1; i < MAXITER && d > LBOUND && t > DBL_EPSILON * d; i++)
d += t *= x * pnonc / (2 * i * (df + 2 * (i - 1)));
}
lua_pushnumber(L, d);
return 1;
}
static int cdf_lgamma (lua_State *L) {
lua_Number x = luaL_checknumber(L, 1);
lua_pushnumber(L, dlngam(&x));
return 1;
}
