\f
/* Statistical calculations. */
-/* Returns the value of the gamma (factorial) function for an integer
+/* Returns the value of the logarithm of gamma (factorial) function for an integer
argument PT. */
static double
-gamma_int (double pt)
+log_gamma_int (double pt)
{
- double r = 1;
+ double r = 0;
int i;
for (i = 2; i < pt; i++)
- r *= i;
+ r += log(i);
+
return r;
}
static inline double
Pr (int a, int b, int c, int d)
{
- return (gamma_int (a + b + 1.) / gamma_int (a + 1.)
- * gamma_int (c + d + 1.) / gamma_int (b + 1.)
- * gamma_int (a + c + 1.) / gamma_int (c + 1.)
- * gamma_int (b + d + 1.) / gamma_int (d + 1.)
- / gamma_int (a + b + c + d + 1.));
+ return exp (log_gamma_int (a + b + 1.) - log_gamma_int (a + 1.)
+ + log_gamma_int (c + d + 1.) - log_gamma_int (b + 1.)
+ + log_gamma_int (a + c + 1.) - log_gamma_int (c + 1.)
+ + log_gamma_int (b + d + 1.) - log_gamma_int (d + 1.)
+ - log_gamma_int (a + b + c + d + 1.));
}
/* Swap the contents of A and B. */
calc_fisher (int a, int b, int c, int d, double *fisher1, double *fisher2)
{
int pt;
+ double pn1;
if (MIN (c, d) < MIN (a, b))
swap (&a, &c), swap (&b, &d);
swap (&a, &c), swap (&b, &d);
}
- *fisher1 = 0.;
- for (pt = 0; pt <= a; pt++)
- *fisher1 += Pr (a - pt, b + pt, c + pt, d - pt);
+ pn1 = Pr (a, b, c, d);
+ *fisher1 = pn1;
+ for (pt = 1; pt <= a; pt++)
+ {
+ *fisher1 += Pr (a - pt, b + pt, c + pt, d - pt);
+ }
*fisher2 = *fisher1;
+
for (pt = 1; pt <= b; pt++)
- *fisher2 += Pr (a + pt, b - pt, c - pt, d + pt);
+ {
+ double p = Pr (a + pt, b - pt, c - pt, d + pt);
+ if (p < pn1)
+ *fisher2 += p;
+ }
}
/* Calculates chi-squares into CHISQ. MAT is a matrix with N_COLS
}
/* Fisher. */
- if (f11 < 5. || f12 < 5. || f21 < 5. || f22 < 5.)
- calc_fisher (f11 + .5, f12 + .5, f21 + .5, f22 + .5, fisher1, fisher2);
+ calc_fisher (f11 + .5, f12 + .5, f21 + .5, f22 + .5, fisher1, fisher2);
}
/* Calculate Mantel-Haenszel. */