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)
