0
$\begingroup$

I am trying to implement a compiled version for the original algorithm that is supposed to run faster . It works fine for small iteration loop number when max=100. However, when loop number gets greater say max=1000 I get the error. I believe it has something to do with machine precision etc. I do not know how to implement MachineInteger or MachineReal in the code. Suggestions?

{* original algorithm *}
max = 1000;
Clear[a, arg1, fn, cpustart]
cpustart = TimeUsed[];
arg1 = Range[0., max - 1, 1.];
fn = Function[{x}, Block[{a = 7.},
 Do[a = 3 a, {i, x}]; a]];
Map[fn, arg1];
(TimeUsed[] - cpustart)

 0.643802

{* compiled version algorithm*}
Clear[a, x, arg1, cfn, cpustart]
cpustart = TimeUsed[];
arg1 = Range[0., max - 1, 1.];
cfn = Compile[{x}, Block[{a = 7.}, Do[a = 3*a, {x}]; a]];
Map[cfn, arg1];
(TimeUsed[] - cpustart)

And the output is,

 CompiledFunction::cfne: Numerical error encountered; proceeding    with uncompiled evaluation.

 CompiledFunction::cfne: Numerical error encountered; proceeding with uncompiled evaluation.

 CompiledFunction::cfne: Numerical error encountered; proceeding with uncompiled evaluation.

 General::stop: Further output of CompiledFunction::cfne will be suppressed during this calculation.

 1.05929
Improve this question
$\endgroup$
5
  • 1
    $\begingroup$ Does this seem relevant to the problems?: 7.*3^999 // Developer`MachineRealQ $\endgroup$
    – Michael E2
    Jul 23, 2022 at 23:28
  • $\begingroup$ Can you please show how to implement MachineRealQ? Did you mean max=1000//Developer`MachnineRealQ? $\endgroup$
    – Aschoolar
    Aug 23, 2022 at 3:18
  • 2
    $\begingroup$ I think I meant that if you keep multiplying 7 by 3 you’ll eventually get a number greater than can be represented by machine real numbers. At that point you get cfne errors. $\endgroup$
    – Michael E2
    Aug 23, 2022 at 3:40
  • $\begingroup$ As almost always, a better algorithm will be much faster than a compiled bad algorithm. Just calling 7*3^Range[0, max-1] is twice as fast as even the compiled code, and does not suffer from machine-precision limits. $\endgroup$
    – Roman
    Aug 23, 2022 at 5:07
  • $\begingroup$ I see, so it is the end results that gives the error. So I should put some kind of code to handle large value of "a". or " a//Developer`MachineRealQ " $\endgroup$
    – Aschoolar
    Aug 23, 2022 at 9:49

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.