Re: Nested iterators in Compile

*To*: mathgroup at smc.vnet.net*Subject*: [mg55019] Re: Nested iterators in Compile*From*: "Carl K. Woll" <carlw at u.washington.edu>*Date*: Thu, 10 Mar 2005 05:24:18 -0500 (EST)*Organization*: University of Washington*References*: <d0mo9g$75h$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Maxim, A workaround that shouldn't affect performance is to write out the nested Do loops explicitly: Compile[{n}, Module[{s = 0}, Do[ Do[s += j, {j, i}], {i, n} ]; s ]][10] The above returned 220 without problems. Carl Woll "Maxim" <ab_def at prontomail.com> wrote in message news:d0mo9g$75h$1 at smc.vnet.net... > The fact that iterators work differently when used in Compile seems to > lead to a serious limitation: > > In[1]:= > Compile[{n}, > Module[{s = 0}, > Do[s += j, {i, n}, {j, i}]; > s > ]][10] > > CompiledFunction::cfse: Compiled expression i should be a machine-size > real number. > > CompiledFunction::cfex: External evaluation error at instruction 4; > proceeding with uncompiled evaluation. > > Out[1]= > 220 > > The iterator {j, i} is evaluated before any value is assigned to i, and > the evaluation of the compiled code fails (and if we add the > initialization i=0 before Do, we'll only get an empty loop as the result, > unlike the uncompiled version). So we have to resort to some workarounds > such as changing the inner iterator to {j, n} and adding If[j>i, > Continue[]] to the loop body, which of course decreases the performance. > > Maxim Rytin > m.r at inbox.ru >