/* POCHISQ -- probability of chi-square value
Adapted from:
Hill, I. D. and Pike, M. C. Algorithm 299
Collected Algorithms for the CACM 1967 p. 243
Updated for rounding errors based on remark in
ACM TOMS June 1985, page 185
*/
double chiAreaRight(double x, int df)
{
const double LOG_SQRT_PI = 0.5723649429247000870717135;
const double I_SQRT_PI = 0.5641895835477562869480795;
double a, y, s;
double e, c, z;
bool even;
if (x <= 0.0 || df < 1) return 1.0;
a = 0.5 * x;
even = (df % 2 == 0);
if (df > 1)
y = ex(-a);
s = even ? y : (2.0 * poz(-sqrt(x)));
if (df > 2)
{
x = 0.5 * (df - 1.0);
z = even ? 1.0 : 0.5;
if (a > BIGX)
{
e = even ? 0.0 : LOG_SQRT_PI;
c = log(a);
while (z <= x)
{
e = log(z) + e;
s += ex(c * z - a - e);
z += 1.0;
}
return s;
}
else
{
e = even ? 1.0 : (I_SQRT_PI / sqrt(a));
c = 0.0;
while (z <= x)
{
e = e * (a / z);
c = c + e;
z += 1.0;
}
return c * y + s;
}
}
else
{
return s;
}
}
quick(int li, int ls, int a[100])
{
if (li < ls)
{
poz(li, ls, &k, a);
quick(li, k-1, a);
quick(k+1, ls, a);
}
return 0;
}
double pochisq(
const double ax, /* obtained chi-square value */
const int df /* degrees of freedom */
)
{
double x = ax;
double a, y, s;
double e, c, z;
int even; /* true if df is an even number */
if (x <= 0.0 || df < 1) {
return 1.0;
}
a = 0.5 * x;
even = (2 * (df / 2)) == df;
y = 0.0;
if (df > 1) {
y = ex(-a);
}
s = (even ? y : (2.0 * poz(-sqrt(x))));
if (df > 2) {
x = 0.5 * (df - 1.0);
z = (even ? 1.0 : 0.5);
if (a > BIGX) {
e = (even ? 0.0 : LOG_SQRT_PI);
c = log(a);
while (z <= x) {
e = log(z) + e;
s += ex(c * z - a - e);
z += 1.0;
}
return (s);
} else {
e = (even ? 1.0 : (I_SQRT_PI / sqrt(a)));
c = 0.0;
while (z <= x) {
e = e * (a / z);
c = c + e;
z += 1.0;
}
return (c * y + s);
}
} else {
return s;
}
}
//
// POCHISQ -- probability of chi-square value
//
// Adapted from:
// Hill, I. D. and Pike, M. C. Algorithm 299
// Collected Algorithms for the CACM 1967 p. 243
// Updated for rounding errors based on remark in
// ACM TOMS June 1985, page 185
//
double pochisq( double x, int df)
{
double a, y, s;
double e, c, z;
bool even; // True if df is an even number
double LOG_SQRT_PI = 0.5723649429247000870717135; // log(sqrt(pi))
double I_SQRT_PI = 0.5641895835477562869480795; // 1 / sqrt(pi)
if (x <= 0.0 || df < 1) {
return 1.0;
}
a = 0.5 * x;
even = !(df % 2);
y = ex(-a);
s = (even ? y : (2.0 * poz(-sqrt(x))));
if (df > 2) {
x = 0.5 * (df - 1.0);
z = (even ? 1.0 : 0.5);
if (a > BIGX) {
e = (even ? 0.0 : LOG_SQRT_PI);
c = log(a);
while (z <= x) {
e = log(z) + e;
s += ex(c * z - a - e);
z += 1.0;
}
return s;
} else {
e = (even ? 1.0 : (I_SQRT_PI /sqrt(a)));
c = 0.0;
while (z <= x) {
e = e * (a / z);
c = c + e;
z += 1.0;
}
return c * y + s;
}
} else {
return s;
}
}
