static int cdf_dbeta (lua_State *L) {
/* stack should contain x, a and b */
lua_Number x = luaL_checknumber(L, 1);
lua_Number a = luaL_checknumber(L, 2);
lua_Number b = luaL_checknumber(L, 3);
check_beta(L, 1, x, a, b);
lua_pushnumber(L, (x==0 || x==1) ? 0 :
exp((a-1)*log(x)+(b-1)*log(1-x)-dlnbet(&a, &b)));
return 1;
}
static int cdf_dnbinom (lua_State *L) {
/* stack should contain s, xn, pr */
lua_Number s = luaL_checknumber(L, 1);
lua_Number xn = luaL_checknumber(L, 2);
lua_Number pr = luaL_checknumber(L, 3);
lua_Number d;
check_nbinom(L, 1, s, xn, pr);
d = exp(xn*log(pr)+s*log(1-pr)-dlnbet(&s, &xn))/s;
lua_pushnumber(L, d);
return 1;
}
static int cdf_dt (lua_State *L) {
/* stack should contain x and df */
lua_Number x = luaL_checknumber(L, 1);
lua_Number df = luaL_checknumber(L, 2);
lua_Number t = 0.5;
lua_Number d;
check_t(L, 1, x, df);
d = df/2;
d = -dlnbet(&d, &t)-(df+1)/2*log(1+x*x/df);
d = exp(d)/sqrt(df);
lua_pushnumber(L, d);
return 1;
}
static int cdf_dbinom (lua_State *L) {
/* stack should contain s, xn, pr */
lua_Number s = luaL_checknumber(L, 1);
lua_Number xn = luaL_checknumber(L, 2);
lua_Number pr = luaL_checknumber(L, 3);
lua_Number d;
check_binom(L, 1, s, xn, pr);
xn -= s;
d = s*log(pr)+xn*log(1-pr);
xn++; s++; /* gamma correction */
d = exp(d-dlnbet(&xn, &s)-log(xn+s-1));
lua_pushnumber(L, d);
return 1;
}
static int cdf_df (lua_State *L) {
/* stack should contain f, dfn, dfd */
lua_Number f = luaL_checknumber(L, 1);
lua_Number dfn = luaL_checknumber(L, 2);
lua_Number dfd = luaL_checknumber(L, 3);
lua_Number df1, df2, r, d;
check_f(L, 1, f, dfn, dfd);
df1 = dfn/2;
df2 = dfd/2;
r = dfn/dfd;
d = df1*log(r)+(df1-1)*log(f);
d -= (df1+df2)*log(1+r*f);
d -= dlnbet(&df1, &df2);
lua_pushnumber(L, exp(d));
return 1;
}
static int cdf_lbeta (lua_State *L) {
lua_Number a = luaL_checknumber(L, 1);
lua_Number b = luaL_checknumber(L, 2);
lua_pushnumber(L, dlnbet(&a, &b));
return 1;
}
static int fchoose (lua_Number n, lua_Number k) {
lua_Number a = n - k + 1;
lua_Number b = k + 1;
return -dlnbet(&a, &b) - log(n + 1);
}
