EGS4 Bug Alert
XYZDOS PRESTA

Status of Bug

This bug has been corrected in the latest unix
(Jan 2, 1997 version 3) and PC distributions of
of the EGS4 code.
This bug alert is for those using the PRESTA version of the xyzdos code (i.e., xyzp.mortran) distributed as xyzdos_presta.tar. A revised/patched version of xyzp.mortran is include in the latest version 3 distribution of the EGS code.

On line 274 of xyzp.mortran: 


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  DO N=2,$MXREG [MED(N)=1;] "I.E. EVERYTHING THE FIRST MEDIUM                 "

                            "CAN BE CHANGED BELOW ON A REGION BY REGION BASIS "

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This should be changed to: 

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  MED(1) = 0; "Set external volume to vacuum"

  DO N=2,$MXREG [MED(N)=1;] "I.E. EVERYTHING THE FIRST MEDIUM                 "

                            "CAN BE CHANGED BELOW ON A REGION BY REGION BASIS "

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  .

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Even with the -static switch thrown (WHICH ALWAYS MUST BE DONE WITH EGS!), some compilers do not zero elements of common areas and this can cause problems with the HOWNEAR routine trying to determine distances to boundaries from outside the target volume, which it was not designed to do.

Bug Fame Goes To...

This bug was originally discovered by Bill Haneman and Lu Wang (Lanzl Institute, Seattle). Thanks also goes to Dave Rogers of the NRC of Canada for related discussion.

This bug alert was posted on the EGS listserver (EGS4-L) by

Alex F Bielajew
30-OCT-1995
Further questions regarding the aforementioned bug should be directed to Alex.

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last updated 09/28/01