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Consider the following input:

temp := c
Manipulate[RegionPlot[True, {a, 0, 1}, {b, 0, temp}], {c, 0, 1}]

I expect to get a region plot with a manipulate slider that I can use to change the domain on the vertical axis. But the slider doesn't do anything and the vertical domain is just stuck at [0,0.0001].

Does anyone know what this isn't working?

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    $\begingroup$ You have a scoping problem, because c in temp := c is not the same as the localized c used in Manipulate. I think the cleanest ways is to use Clear[temp]; temp[c_] := c, then Manipulate[RegionPlot[True, {a, 0, 1}, {b, 0, temp[c]}], {c, 0, 1}]. $\endgroup$ Commented Jun 10, 2024 at 13:38
  • $\begingroup$ @Domen thanks. Is there a reason you didn't post this as an answer? Also, would it be possible to explain (or to point to an explanation) why temp:=c and temp[c_]:=c produce different behaviour? I had thought the only difference was one of syntax: the latter allows you to specify the arguments of temp when calling it. $\endgroup$ Commented Jun 11, 2024 at 9:41
  • $\begingroup$ Because it's a common mistake and questions like this appear sporadically here, but I wasn't in a mood to search for an exact duplicate to close the question :) $\endgroup$ Commented Jun 11, 2024 at 10:09
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    $\begingroup$ Does this answer your question? How are parameters evaluated for a Plot in Manipulate See also section Possible issues in the documentation for Manipulate. $\endgroup$ Commented Jun 11, 2024 at 10:09
  • $\begingroup$ @Domen yes, it does thanks. $\endgroup$ Commented Jun 11, 2024 at 10:35

1 Answer 1

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I think you need to bring temp into the Manipulate, e.g:

Manipulate[
 RegionPlot[True, {a, 0, 1}, {b, 0, temp}],
 {temp, 0.1, 1}]

enter image description here

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  • $\begingroup$ Thanks, yes. But my problem is that my application temp is not a simple constant but rather a complicated function of c defined elsewhere in the notebook. I don't want to copy the whole thing when it seems like I should be able to refer to the relevant expression by its variable name. $\endgroup$ Commented Jun 10, 2024 at 13:18

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