def pdtrc(k, m): """Returns sum of right tail of Poisson distribution, k+1 through infinity. See Cephes docs for details. """ if k < 0: raise ValueError, "Poisson k must be >= 0." if m < 0: raise ValueError, "Poisson m must be >= 0." return igam(k+1, m)
def chi_low(x, df): """Returns left-hand tail of chi-square distribution (0 to x), given df. x ranges from 0 to infinity. df, the degrees of freedom, ranges from 1 to infinity (assume integers). Typically, df is (r-1)*(c-1) for a r by c table. Result ranges from 0 to 1. See Cephes docs for details. """ x = fix_rounding_error(x) if x < 0: raise ValueError, "chi_low: x must be >= 0 (got %s)." % x if df < 1: raise ValueError, "chi_low: df must be >= 1 (got %s)." % df return igam(df/2, x/2)
def gdtr(a, b, x): """Returns integral from 0 to x of Gamma distribution with params a and b. """ if x < 0.0: return ZeroDivisionError, "x must be at least 0." return igam( b, a * x)