4
$\begingroup$

Bug introduced in 12.1 or earlier and persisting through 13.0

Consider the following region:

region = BooleanRegion[#1 || #2 &, {Circle[{0, 0}, 
   63.01771474209481`, {-0.3085423746716913`, 0}], 
  Circle[{0, 0}, 63.01771474209481`, {0, 0.3085423746716913`}]}]

Why in Mathematica 12.1 RegionMeasure[region] returns a complex value, and how to avoid it without dealing with explicit calculations (despite the fact that it is possible to make this easily)?

RegionMeasure[region]

38.8873 + 0.0000128693 I

Improve this question
$\endgroup$
3
  • $\begingroup$ Machine precision calculations neither track nor control precision. You get what you get. Arbitrary precision will track and attempt to control precision. Exact numbers will give exact results. $\endgroup$
    – Bob Hanlon
    Feb 4 at 15:50
  • $\begingroup$ Per the tag wiki for bugs: "Please do not use this tag for new questions." -- Now, does the community think it's a bug? $\endgroup$
    – Michael E2
    Feb 4 at 18:00
  • $\begingroup$ I think it is a bug. Worth reporting to the support. Added the BUG header and the tag. $\endgroup$
    – Alexey Popkov
    Feb 5 at 4:03

1 Answer 1

Reset to default
5
$\begingroup$

This is numerical inaccuracy stemming from your machine precision inputs. Setting a WorkingPrecision for RegionMeasure takes care of the problem:

RegionMeasure[region, WorkingPrecision -> 10]

(* Out: 38.88727071 *)
```
Improve this answer
$\endgroup$
3
  • 1
    $\begingroup$ Why not WorkingPrecision -> $MachinePrecision? (Why so much less than?) -- Oh, bizarre. It makes no difference. But I usually use WorkingPrecision -> 16 because it's shorter to type, and that works. -- Oh, wow, WorkingPrecision -> 10. fails, too. That's wierd. $\endgroup$
    – Michael E2
    Feb 4 at 18:00
  • 2
    $\begingroup$ Hmm, WorkingPrecision -> p seems to work only if p is an integer (fails for Real and Rational). $\endgroup$
    – Michael E2
    Feb 4 at 18:07
  • $\begingroup$ @MichaelE2 This looks like a bug in WorkingPrecision functionality. Worth reporting to support. $\endgroup$
    – Alexey Popkov
    Feb 5 at 3:58

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.