Re: Re: Set::setraw error

*To*: mathgroup at smc.vnet.net*Subject*: [mg90382] Re: [mg90352] Re: [mg90326] Set::setraw error*From*: DrMajorBob <drmajorbob at att.net>*Date*: Tue, 8 Jul 2008 02:24:21 -0400 (EDT)*References*: <32330841.1215353835393.JavaMail.root@m08>*Reply-to*: drmajorbob at longhorns.com

Sorry again, the infinite loop was cause by my leaving out initializations for x, y, and r. Clear[a, b, xgcd] xgcd[0, 0] = {0, 0, 1}; xgcd[0, b_] = {Abs@b, 0, Sign@b}; xgcd[a_, 0] = {Abs@a, Sign@a, 0}; xgcd[aa_, bb_] := Module[{a = Abs@aa, b = Abs@bb, x = 1, y = 0, r = 0, s = 1, c, q}, While[b != 0, {c, q} = {Mod[a, b], Quotient[a, b]}; {a, b, r, s, x, y} = {b, c, x - q*r, y - q*s, r, s}]; {a, x*Sign@aa, y*Sign@bb}] xgcd[2, 3] {1, -1, 1} Bobby On Mon, 07 Jul 2008 11:46:12 -0500, DrMajorBob <drmajorbob at att.net> wrote: > I had a copying error or something that duplicated the line > > xgcd[aa_,bb_]:=Module[{a=Abs@aa,b=Abs@bb}, > > Take one of them out. > > Bobby > > On Mon, 07 Jul 2008 04:05:31 -0500, DrMajorBob <drmajorbob at att.net> > wrote: > >> The error message tells you that you can't Set variables used as >> arguments, in this case a=-a, for instance. >> >> There are other problems, including the fact that x, y, and r are >> undefined the first time you use them in >> >> {a, b, r, s, x, y} = {b, c, x - q*r, y - q*s, r, s} >> >> which means (if you get rid of the "setraw" error), that statement will >> be >> an infinite loop all by itself. >> >> If we knew what you were trying to accomplish, we might go farther, but >> for now I'll show you a partial solution WITH the infinite loop still >> present: >> >> Clear[a,b,xgcd] >> xgcd[0,0]={0,0,1}; >> xgcd[0,b_]={Abs@b,0,Sign@b}; >> xgcd[a_,0]={Abs@a,Sign@a,0}; >> xgcd[aa_,bb_]:=Module[{a=Abs@aa,b=Abs@bb}, >> xgcd[aa_, bb_] := Module[{a = Abs@aa, b = Abs@bb}, >> While[b != 0, >> {c, q} = {Mod[a, b], Quotient[a, b]}; >> Print@{c, q}; >> {a, b, r, s, x, y} = {b, c, x - q*r, y - q*s, r, s}]; >> {a, x*Sign@aa, y*Sign@bb} >> ] >> xgcd[2,3] >> >> {2,0} >> $IterationLimit::itlim: Iteration limit of 4096 exceeded. >> >> $IterationLimit::itlim: Iteration limit of 4096 exceeded. >> >> $IterationLimit::itlim: Iteration limit of 4096 exceeded. >> >> General::stop: Further output of $IterationLimit::itlim will be >> suppressed >> during this calculation. >> >> {1,1} >> {0,2} >> {1,-Hold[r]+Hold[x],-Hold[s]+Hold[y]} >> >> Notice I've changed the structure of the function to one that's much >> clearer (IMHO). >> >> To become proficient in Mathematica you need to, among other things, >> erase >> Return from your memory. >> >> Never use it again. EVER. >> >> Bobby >> >> On Sun, 06 Jul 2008 06:17:46 -0500, Steven Siew <stevensiew2 at gmail.com> >> wrote: >> >>> I have encountered this Set:setraw error for the code below. >>> >>> I'm stumped. Does anyone have any idea what went wrong? >>> >>> xgcd[a_,b_]:=Module[{xsign=1,ysign=1,x=1,y=0,r=0,s=1,c,q}, >>> If[a == 0 && b == 0,Return[{0,0,1}]]; >>> If[a == 0,Return[{Abs[b],0,b/Abs[b]}] ]; >>> If[b == 0,Return[{Abs[a],a/Abs[a],0}]]; >>> If[a<0,a=-a; xsign=-1]; >>> If[b<0,b=-b; ysign=-1]; >>> While[b\[NotEqual]0, >>> {c,q}={Mod[a,b],Quotient[a,b]}; >>> {a,b,r,s,x,y}={b,c,x-q*r,y-q*s,r,s} >>> ]; >>> Return[{a,x*xsign,y*ysign}] >>> ] >>> >>> xgcd[2, 3] >>> >>> \!\(\* >>> RowBox[{\(Set::"setraw"\), \(\(:\)\(\ \)\), "\<\"Cannot assign to >>> raw \ >>> object \\!\\(2\\). \\!\\(\\*ButtonBox[\\\"More\[Ellipsis]\\\", \ >>> ButtonStyle->\\\"RefGuideLinkText\\\", ButtonFrame->None, \ >>> ButtonData:>\\\"Set::setraw\\\"]\\)\"\>"}]\) >>> >>> >> >> >> > > > -- DrMajorBob at longhorns.com