Category : Pascal Source Code
Archive   : PIBSIGS.ZIP
Filename : SIGCHI.PAS

(*-------------------------------------------------------------------------*)
(* SigChi -- Significance of Chi-Square distribution *)
(*-------------------------------------------------------------------------*)

FUNCTION SigChi( Chisq , Df : REAL ) : REAL;

(*-------------------------------------------------------------------------*)
(* *)
(* Function: SigChi *)
(* *)
(* Purpose: Evaluates Chi-Square distribution probability *)
(* *)
(* Calling Sequence: *)
(* *)
(* P := SigChi( Chisq , Df ); *)
(* *)
(* Chisq --- Chi-square value *)
(* Df --- Degrees of freedom *)
(* *)
(* P --- Resultant probability *)
(* *)
(* Calls: *)
(* *)
(* GammaIn *)
(* *)
(* Method: *)
(* *)
(* The input values are transformed to match the *)
(* requirements of the Gamma distribution. Function GammaIn *)
(* provides the corresponding cumulative incomplete gamma *)
(* probability. *)
(* *)
(* An error in the input arguments results in a returned *)
(* probability of -1. *)
(* *)
(*-------------------------------------------------------------------------*)

CONST
MaxIter = 200;
Dprec = 12;

VAR
Ierr: INTEGER;
Iter: INTEGER;
Cprec: REAL;

BEGIN (* SigChi *)

SigChi := 1.0 - GammaIn( Chisq / 2.0, Df / 2.0, Dprec, MaxIter,
Cprec, Iter, Ierr );

IF ( Ierr <> 0 ) THEN SigChi := -1.0;

END (* SigChi *);