From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/gresid.f_ix86_Linux | 74 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 src/slalib/gresid.f_ix86_Linux (limited to 'src/slalib/gresid.f_ix86_Linux') diff --git a/src/slalib/gresid.f_ix86_Linux b/src/slalib/gresid.f_ix86_Linux new file mode 100644 index 0000000..ec93bdd --- /dev/null +++ b/src/slalib/gresid.f_ix86_Linux @@ -0,0 +1,74 @@ + REAL FUNCTION sla_GRESID (S) +*+ +* - - - - - - - +* G R E S I D +* - - - - - - - +* +* Generate pseudo-random normal deviate ( = 'Gaussian residual') +* (single precision) +* +* !!! Version for Linux !!! +* +* Given: +* S real standard deviation +* +* The results of many calls to this routine will be +* normally distributed with mean zero and standard deviation S. +* +* The Box-Muller algorithm is used. This is described in +* Numerical Recipes, section 7.2. +* +* B.K.McIlwrath Starlink 12 January 1996 +*- + + IMPLICIT NONE + + REAL S + + REAL X,Y,R,W,GNEXT,G + LOGICAL FTF,FIRST + + REAL RANDOM + + SAVE GNEXT,FTF,FIRST + DATA FTF,FIRST / .TRUE.,.TRUE. / + +* First time through, initialise the random-number generator + IF (FTF) THEN + X = RANDOM(12345678) + FTF = .FALSE. + END IF + +* Second normal deviate of the pair available? + IF (FIRST) THEN + +* No - generate two random numbers inside unit circle + R = 2.0 + DO WHILE (R.GE.1.0) + +* Generate two random numbers in range +/- 1 + X = 2.0*RANDOM(0)-1.0 + Y = 2.0*RANDOM(0)-1.0 + +* Try again if not in unit circle + R = X*X+Y*Y + END DO + +* Box-Muller transformation, generating two deviates + W = SQRT(-2.0*LOG(R)/MAX(R,1E-20)) + GNEXT = X*W + G = Y*W + +* Set flag to indicate availability of next deviate + FIRST = .FALSE. + ELSE + +* Return second deviate of the pair & reset flag + G = GNEXT + FIRST = .TRUE. + END IF + +* Scale the deviate by the required standard deviation + sla_GRESID = G*S + + END -- cgit