Re: Re: Re: Slowdown

*To*: mathgroup at smc.vnet.net*Subject*: [mg53278] Re: [mg53254] Re: [mg53241] Re: Slowdown*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Tue, 4 Jan 2005 03:13:00 -0500 (EST)*References*: <cr33tt$je6$1@smc.vnet.net> <200501020912.EAA27775@smc.vnet.net> <200501030929.EAA10649@smc.vnet.net> <C570DAF1-5D86-11D9-8B6F-000A95B4967A@mimuw.edu.pl>*Sender*: owner-wri-mathgroup at wolfram.com

I just noticed another thing, which seems to throw more light at what is happenng. Look carefully at the Hash values of the different names of the form weirdness$number: MapIndexed[{First[#2], Hash[#1]} & , ToExpression /@ (StringJoin["weirdness", "$", ToString[#1]] & ) /@ Range[20]] {{1, 1783099877}, {2, 1783099878}, {3, 1783099879}, {4, 1783099880}, {5, 1783099881}, {6, 1783099882}, {7, 1783099883}, {8, 1783099884}, {9, 1783099885}, {10, 667842086}, {11, 667842087}, {12, 667842088}, {13, 667842089}, {14, 667842090}, {15, 667842091}, {16, 667842092}, {17, 667842093}, {18, 667842094}, {19, 667842095}, {20, 667843323}} You can see a big jump in the hash value at weirdness$10. That is exactly the point at which the slowdown occurs. Andrzej Kozlowski On 3 Jan 2005, at 21:55, Andrzej Kozlowski wrote: > I can't see any siginificant slowdowns demonstrated by your code. The > differences in timings between different combinations seem > insignificant. Cna you suggest any other name but "weirdness" that > shows significant slowdown? > > Besides, using Module only obsures what is really happening. Module > simply renames local variables by appending $somenumber to their name > but the "number" that is used is different each time. You can do that > whiteout Module and see exactly which names produce the slowdown > effect. It seems that the names weirdness$1 to weirdness$9 do not. > > In[1]:= > L=weirdness$1[]; > Do[L=weirdness$1[L,i],{i,10^4}]//Timing > > Out[2]= > {0.03 Second,Null} > > In[3]:= > L=weirdness$9[]; > Do[L=weirdness$9[L,i],{i,10^4}]//Timing > > Out[4]= > {0.08 Second,Null} > > The problem seems to begin with weirdness$10 > > In[5]:= > L=weirdness$10[]; > Do[L=weirdness$10[L,i],{i,10^4}]//Timing > > Out[6]= > {13.2 Second,Null} > > and continues for higher values, as far as I have checked. > > When you run Module with a fresh Kernel Mathematica seems to always > begin by appending $17: > > In[1]:= > Module[{weirdness, L}, > L = weirdness[]; > Do[L = weirdness[L, i], {i, 1}] > ] // Trace > > Out[1]= > {Module[{weirdness,L},L=weirdness[];Do[L=weirdness[L,i],{i,1}]],{L$17=\ > weirdness$17[];Do[L$17=weirdness$17[L$17, > > i],{i,1}],{L$17=weirdness$17[],weirdness$17[]},{Do[L$17=weirdness$17[L$ > \ > 17,i],{i,1}],{{{L$17,weirdness$17[]},{i,1},weirdness$17[weirdness$17[], > > 1]},L$17=weirdness$17[weirdness$17[],1],weirdness$17[weirdness$17[],1]\ > },Null},Null},Null} > > on subsequent runs this is increased: > > In[2]:= > Module[{weirdness, L}, > L = weirdness[]; > Do[L = weirdness[L, i], {i, 1}] > ] // Trace > > Out[2]= > {Module[{weirdness,L},L=weirdness[];Do[L=weirdness[L,i],{i,1}]],{L$19=\ > weirdness$19[];Do[L$19=weirdness$19[L$19, > > i],{i,1}],{L$19=weirdness$19[],weirdness$19[]},{Do[L$19=weirdness$19[L$ > \ > 19,i],{i,1}],{{{L$19,weirdness$19[]},{i,1},weirdness$19[weirdness$19[], > > 1]},L$19=weirdness$19[weirdness$19[],1],weirdness$19[weirdness$19[],1]\ > },Null},Null},Null} > > in any case all these numbers are larger than 10 and produce slowdown, > but the numbers 10-16 which never occur inside Module also suffer form > this problem: > > In[3]:= > L=weirdness$11[]; > Do[L=weirdness$11[L,i],{i,10^4}]//Timing > > Out[4]= > {13.1 Second,Null} > > In[5]:= > L=weirdness$16[]; > Do[L=weirdness$16[L,i],{i,10^4}]//Timing > > Out[6]= > {14.62 Second,Null} > > However, I have not been able to find any other name but weirdness > that produces this effect. This seems weird. > > Andrzej Kozlowski > > > > On 3 Jan 2005, at 18:29, yehuda ben-shimol wrote: > >> Hi Roland, >> I'm afraid this is not true. Just try to run the code I sent with my >> post. "weirdness" was time consuming while weirdness1 was not. In >> addition it happened (not consistently) that function name of a SINGLE >> character suffered from this behavior as well. >> the code is given below for your convenience. >> >> t = CharacterRange["a", "z"]; >> Do[fname = StringJoin[t[[Table[Random[Integer, {1,26}], {i}]]]]; >> Print[i, "\t", fname, "\t", >> Timing[ >> Module[{fs = ToExpression[fname], L}, >> L = fs[]; >> Do[L = fs[L, j], {j, 104}]]]], {i, 1, 50}, {5}] >> >> >> yehuda >> >> Roland Franzius wrote: >> >>> Maxim wrote: >>> >>> >>>> Consider: >>>> >>>> In[1]:= >>>> Module[{f, L}, >>>> L = f[]; >>>> Do[L = f[L, i], {i, 10^4}] >>>> ] // Timing >>>> >>>> Module[{weirdness, L}, >>>> L = weirdness[]; >>>> Do[L = weirdness[L, i], {i, 10^4}] >>>> ] // Timing >>>> >>>> Out[1]= >>>> {0.015*Second, Null} >>>> >>>> Out[2]= >>>> {3.063*Second, Null} >>>> >>>> Here the timings differ by a factor of 200. Besides, the timing >>>> grows >>>> linearly in the first case and quadratically in the second >>>> (therefore, for >>>> n=10^5 there will be an approximately 2000 times slowdown). We can >>>> only >>>> guess that something goes wrong with the symbol name hashing. >>>> >>>> >>> >>> The timing difference occurs when the symbol "wierdness" exceeds 8 >>> characters. Test it for "wierdnes". That seems to be a consequence of >>> the machine routine for string comparison. Up to 8 characters can be >>> used without using a memory to memory compare. Of course it should be >>> possible to write a compare routine that makes not such a bit step. >>> >> >

**Follow-Ups**:**Re: Re: Re: Re: Slowdown***From:*DrBob <drbob@bigfoot.com>

**References**:**Re: Slowdown***From:*Roland Franzius <roland.franzius@uos.de>

**Re: Re: Slowdown***From:*yehuda ben-shimol <benshimo@bgu.ac.il>