Re: Compile forgets assigned values inside Do unless they are initialised

*To*: mathgroup at smc.vnet.net*Subject*: [mg82343] Re: Compile forgets assigned values inside Do unless they are initialised*From*: Vince Virgilio <blueschi at gmail.com>*Date*: Thu, 18 Oct 2007 04:49:00 -0400 (EDT)*References*: <fepss7$gi3$1@smc.vnet.net><ff1pcn$8p2$1@smc.vnet.net>

On Oct 16, 3:31 am, "Jean-Marc Gulliet" <jeanmarc.gull... at gmail.com> wrote: > Giving more thoughts, I think you are right and my "thesis" would have > been clearer if I had written, "As a rule of thumb, if one wants to > compile an expression that uses local symbols, then these symbols > should be initialized preferably at the beginning of the Module or > Block construct, or as soon as possible." > > Why that? Because, as we are warned by the online documentation, > "Compiled code does not handle numerical precision and local variables > in the same way as ordinary Mathematica code." > > Moreover, "The number of times and the order in which objects are > evaluated by Compile may be different from ordinary Mathematica code." > > In other words, ordinary evaluation rules do not necessarily and/or > usually apply to compiled code. I second this. Here's another example with similar behavior, but with Compile at level > 0. In[5]:= Module[{x},Compile[{},x=7;];x] Module[{x=0},Compile[{},x=7;];x] Out[5]= x$178 Out[6]= 0 Notice that it does not produce messages. Beware. Vince Virgilio