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.TH cdfgam 1 "Dec 1997" "Scilab Group" "Scilab Function"
.so ../sci.an
.SH NAME
cdfgam - cumulative distribution function gamma distribution
.SH CALLING SEQUENCE
.nf
[P,Q]=cdfgam("PQ",X,Shape,Scale)
[X]=cdfgam("X",Shape,Scale,P,Q)
[Shape]=cdfgam("Shape",Scale,P,Q,X)
[Scale]=cdfgam("Scale",P,Q,X,Shape)
.fi
.SH PARAMETERS
.TP 10
P,Q,X,Shape,Scale
: five real vectors of the same size.
.TP
P,Q (Q=1-P)
The integral from 0 to X of the gamma density.
Input range: [0,1].
.TP
X
: The upper limit of integration of the gamma density.
Input range: [0, +infinity).
Search range: [0,1E300]
.TP
Shape
: The shape parameter of the gamma density.
Input range: (0, +infinity).
Search range: [1E-300,1E300]
.TP
Scale
: The scale parameter of the gamma density.
Input range: (0, +infinity).
Search range: (1E-300,1E300]
.SH DESCRIPTION
Calculates any one parameter of the gamma
distribution given values for the others.
.LP
Cumulative distribution function (P) is calculated directly by
the code associated with:
.LP
DiDinato, A. R. and Morris, A. H. Computation of the incomplete
gamma function ratios and their inverse. ACM Trans. Math.
Softw. 12 (1986), 377-393.
.LP
Computation of other parameters involve a seach for a value that
produces the desired value of P. The search relies on the
monotinicity of P with the other parameter.
.LP
The gamma density is proportional to
\fVT**(SHAPE - 1) * EXP(- SCALE * T)\fR
.LP
From DCDFLIB: Library of Fortran Routines for Cumulative Distribution
Functions, Inverses, and Other Parameters (February, 1994)
Barry W. Brown, James Lovato and Kathy Russell. The University of
Texas.
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