def pdtr(k, m):
"""Returns sum of left tail of Poisson distribution, 0 through k.
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 igamc(k + 1, m)
def chi_high(x, df):
"""Returns right-hand tail of chi-square distribution (x 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_high: x must be >= 0 (got %s)." % x)
if df < 1:
raise ValueError("chi_high: df must be >= 1 (got %s)." % df)
return igamc(df / 2, x / 2)
def gdtrc(a, b, x):
"""Returns integral from x to inf of Gamma distribution with params a and b.
"""
if x < 0.0:
raise ZeroDivisionError("x must be at least 0.")
return igamc(b, a * x)
