43 lines
3.1 KiB
Rexx
43 lines
3.1 KiB
Rexx
/*REXX program demonstrates an evolutionary algorithm (by using mutation). */
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parse arg children MR seed . /*get optional arguments from the C.L. */
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if children=='' then children = 10 /*# children produced each generation. */
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if MR =='' then MR = "4%" /*the character Mutation Rate each gen.*/
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if right(MR,1)=='%' then MR=strip(MR,,"%")/100 /*expressed as a percent? Then adjust.*/
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if seed\=='' then call random ,,seed /*SEED allow the runs to be repeatable.*/
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abc = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ '; Labc=length(abc)
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do i=0 for Labc /*define array (for faster compare), */
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@.i=substr(abc, i+1, 1) /* it's better than picking out a */
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end /*i*/ /* byte from a character string. */
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target= 'METHINKS IT IS LIKE A WEASEL' ; Ltar=length(target)
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do i=1 for Ltar /*define an array (for faster compare),*/
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T.i=substr(target, i, 1) /* it's better than a byte-by-byte */
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end /*i*/ /* compare using character strings.*/
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parent= mutate( left('', Ltar), 1) /*gen rand string, same length as tar. */
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say center('target string', Ltar, "─") 'children' "mutationRate"
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say target center(children, 8) center((MR*100/1)'%',12); say
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say center('new string' , Ltar, "─") 'closeness' "generation"
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do gen=0 until parent==target; close=fitness(parent)
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almost=parent
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do children; child=mutate(parent,MR)
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_=fitness(child); if _<=close then iterate
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close=_; almost=child
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say almost right(close, 9) right(gen, 10)
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end /*children*/
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parent=almost
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end /*gen*/
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exit /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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fitness: parse arg x; $=0; do k=1 for Ltar; $=$+(substr(x,k,1)==T.k); end; return $
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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mutate: parse arg x,rate /*set X to 1st argument, RATE to 2nd.*/
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$=; do j=1 for Ltar; r=random(1, 100000) /*REXX's max for RANDOM*/
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if .00001*r<=rate then do; _=r//Labc; $=$ || @._; end
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else $=$ || substr(x, j, 1)
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end /*j*/
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return $
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