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[u/mrichter/AliRoot.git] / PDF / spdf / valdis.F

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+*
+* $Id$
+*
+* $Log$
+* Revision 1.1.1.2  1996/10/30 08:31:58  cernlib
+* Version 7.04
+*
+* Revision 1.1.1.1  1996/04/12 15:30:07  plothow
+* Version 7.01
+*
+*
+#include "pdf/pilot.h"
+C----------------------------------------------------------------------
+      FUNCTION VALDIS(XX)
+      COMMON/W5051I2/ Q2L
+      PARAMETER (Q02=0.5,ALAM2=0.045*0.045)
+      PARAMETER (AL0=0.7, BET0=3.21, ALPRM=-0.19, BETPRM=0.82)
+
+      DATA ZERO/0./,HALF/0.5/,ONE/1./,TWO/2./,THRE/3./
+      DATA IRAZ/0/, Q2OLD/-1./
+      SAVE AV, ALPHA, BETA
+
+      IF(Q2L.NE.Q2OLD) THEN
+          Q2OLD = Q2L
+          S     = LOG( LOG( MAX( Q02,Q2L)/ALAM2)/ LOG( Q02/ALAM2))
+          ALPHA = AL0  + ALPRM *S
+          BETA  = BET0 + BETPRM*S
+          AV    = THRE*GAMMA(ALPHA+BETA+ONE)/
+     1                                 (GAMMA(ALPHA)*GAMMA(BETA+ONE))
+      ENDIF
+      VALDIS=AV * XX**ALPHA * (ONE-XX)**BETA
+      RETURN
+      END