scipy.special.chdtr

scipy.special.chdtr(x1, x2[, out])

p=chdtr(v,x) Returns the area under the left hand tail (from 0 to x) of the Chi square probability density function with v degrees of freedom: 1/(2**(v/2) * gamma(v/2)) * integral(t**(v/2-1) * exp(-t/2), t=0..x)