Speed (resumed)

*To*: mathgroup at smc.vnet.net*Subject*: [mg15732] Speed (resumed)*From*: tobiasoed at my-dejanews.com*Date*: Fri, 5 Feb 1999 03:42:26 -0500 (EST)*Organization*: Deja News - The Leader in Internet Discussion*Sender*: owner-wri-mathgroup at wolfram.com

Hi all, continuing on the speed of evaluation started in another thread about the difference between Do and Nest, I was wondering what you thought about the difference in evaluation time between pure functions written as (something depending on #i) & and Function[{vars},samething depending on vars] In[1]:= Timing[x=0.3;Print[x];Nest[# 1.003456 &,x,1000000]] 0.3 Out[1]= {56.8977 Second, 6.47467520 10*^1497} In[2]:= Timing[x=0.3;Print[x];Nest[Function[{y},y 1.003456],x,1000000]] 0.3 Out[2]= {79.2468 Second, 6.47467520 10*^1497} Using the Function notation increases the evaluation time by 40 %. I kind of understand this since in the Function case there has to be a replacement between the formal parameters and the arguments to be made which is not as streight forward as a replacement of #i by the arguments. On the other hand, I do not get at all the difference in evaluation time between Map[f,expr] and f /@ expr In[3]:= Timing[Map[(#*2)&,Table[i,{i,10000}]]][[1]] Out[3]= 1.63 Second In[4]:= Timing[(#*2)& /@ Table[i,{i,10000}]][[1]] Out[4]= 1.55 Second 10 times more In[5]:= Timing[Map[(#*2)&,Table[i,{i,100000}]]][[1]] Out[5]= 16.31 Second In[6]:= Timing[(#*2)& /@ Table[i,{i,100000}]][[1]] Out[7]= 15.44 Second I expected that Map[] would be slower by a constant amount of time used for the translation to the other form but no it's more or less linear... I'd like to know if anyone knew other tricks that reduce computation time just by changing the notation ? Tobias -----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own