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cumgamma(x,alpha [,upper:T or lower:F]), x and alpha REAL, elements of
  alpha > 0

Keywords: probabilities
cumgamma(Val,alpha) computes the probabilities that a gamma random
variable with shape parameter alpha would be less than the elements of
the vector, matrix, or array Val.

When Val and alpha are both not scalars, they must be vectors, matrices,
or arrays with the same size and shape which will also be the size and
shape of the result.

The elements of alpha must be positive.

cumgamma(Val,alpha,upper:T) and cumgamma(Val,alpha,lower:F) compute
upper tail probabilities.  For large Val, this may provide more
significant digits than the mathematically equivalent 1 -

cumchi(x,df [,upper:T or lower:F]) is equivalent to cumgamma(x/2,df/2
[,upper:T or lower:F]).

  Cmd> 1 - cumgamma(13.27, 15.5) # P(x >= 13.27)
  (1)      0.69507

  Cmd> cumgamma(13.27, 15.5, upper:T) # the same
  (1)      0.69507

See also invgamma(), cumchi(), invchi().

Gary Oehlert 2003-01-15