Re: Re: Set::setraw error

*To*: mathgroup at smc.vnet.net*Subject*: [mg90379] Re: [mg90352] Re: [mg90326] Set::setraw error*From*: DrMajorBob <drmajorbob at att.net>*Date*: Tue, 8 Jul 2008 02:23:47 -0400 (EDT)*References*: <32330841.1215353835393.JavaMail.root@m08>*Reply-to*: drmajorbob at longhorns.com

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