gamcdf
              "upper")"upper")Gamma cumulative distribution function (CDF).
For each element of x, compute the cumulative distribution function (CDF) of the Gamma distribution with shape parameter a and scale parameter b. When called with only one parameter, then b defaults to 1. The size of p is the common size of x, a, and b. A scalar input functions as a constant matrix of the same size as the other inputs.
 When called with three output arguments, i.e. [p, plo,
 pup], gamcdf computes the confidence bounds for p when
 the input parameters a and b are estimates.  In such case,
 pcov, a  matrix containing the covariance matrix of the
 estimated parameters, is necessary.  Optionally, alpha, which has a
 default value of 0.05, specifies the 100 * (1 - alpha) percent
 confidence bounds.  plo and pup are arrays of the same size as
 p containing the lower and upper confidence bounds.
 […] = gamcdf (…, "upper") computes the upper tail
 probability of the Gamma distribution with parameters a and
 b, at the values in x.
OCTAVE/MATLAB use the alternative parameterization given by the pair , i.e. shape a and scale b. In Wikipedia, the two common parameterizations use the pairs , as shape and scale, and , as shape and rate, respectively. The parameter names a and b used here (for MATLAB compatibility) correspond to the parameter notation instead of the as reported in Wikipedia.
Further information about the Gamma distribution can be found at https://en.wikipedia.org/wiki/Gamma_distribution
See also: gaminv, gampdf, gamrnd, gamfit, gamlike, gamstat
Source Code: gamcdf
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 ## Plot various CDFs from the Gamma distribution
 x = 0:0.01:20;
 p1 = gamcdf (x, 1, 2);
 p2 = gamcdf (x, 2, 2);
 p3 = gamcdf (x, 3, 2);
 p4 = gamcdf (x, 5, 1);
 p5 = gamcdf (x, 9, 0.5);
 p6 = gamcdf (x, 7.5, 1);
 p7 = gamcdf (x, 0.5, 1);
 plot (x, p1, "-r", x, p2, "-g", x, p3, "-y", x, p4, "-m", ...
       x, p5, "-k", x, p6, "-b", x, p7, "-c")
 grid on
 legend ({"α = 1, β = 2", "α = 2, β = 2", "α = 3, β = 2", ...
          "α = 5, β = 1", "α = 9, β = 0.5", "α = 7.5, β = 1", ...
          "α = 0.5, β = 1"}, "location", "southeast")
 title ("Gamma CDF")
 xlabel ("values in x")
 ylabel ("probability")
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