Variable scoping in Manipulate

Question

Here is my attempt to manipulate the value of q for the PDF function. Whenever I use the manipulate function, nothing happens to the output. Can anyone explain why?

David G. Stork · Accepted Answer · 2018-09-15T20:42:10.313

3

You have many code errors, such as the error in defining a function G[x_]= instead of G[x_]:=, the fact that sigma cannot have a value (because q is not assigned), missing semicolons, and much more.

I presume you're lifting my code from here.

Anyway, here is your answer:

Manipulate[
 Integrate[
  PDF[
      NormalDistribution[0, -q Log[2, q] - (1 - q) Log[2, 1 - q]], x], 
  {x, 0, 1}], 
  {q, .1, .3}]

edited Sep 15 '18 at 20:42

answered Sep 15 '18 at 20:20

David G. Stork

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Yes, I was the one who asked the previous question as well. – sde7 Sep 15 '18 at 20:28
1

...and never accepted my previous answer. – David G. Stork Sep 15 '18 at 20:32
I just recently made an account. – sde7 Sep 15 '18 at 20:36

score 1 · Answer 2 · answered Sep 15 '18 at 20:14

You have a variable scoping problem. The global q that appears in your definition of sigma is not the same as the local q that appears in your Manipulate expression. One way to fix it is:

sigma[q_] := -q Log2[q] - (1 - q) Log2[1 - q]
g[q_][x_] := PDF[NormalDistribution[0, sigma[q]], x]
Manipulate[g[q][x], {q, .0001, 1}]

score 0 · Answer 3 · answered Sep 15 '18 at 20:11

0

Manipulate doesn't "see" the q term in the argument.

To fix this use

Manipulate[PDF[NormalDistribution[0, sigma], x] /. q -> Q, {Q, 0, 1}]

Or make sigma a function of q as

sigma[q_] := -q Log[2, q] - (1 - q) Log[2, 1 - q]
Manipulate[PDF[NormalDistribution[0, sigma[q]], x], {q, 0, 1}]

answered Sep 15 '18 at 20:11

NonDairyNeutrino

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I made this change. It does work. However, part of the input is to integrate the PDF function G[x]. It does not make the change in Out[54] whenever I manipulate q. Any ideas? – sde7 Sep 15 '18 at 20:23

Variable scoping in Manipulate

3 Answers3