Plotting function with unique symbols

Question

I would like to plot a function which involves multiple symbols created using Unique. Consider the following simple example.

X = {Unique["x"]}
Plot[Evaluate[2 X[[1]]], {Evaluate[X[[1]]], 0, 1}]

Unfortunately, this results in an error Plot::write: "Tag Evaluate in Evaluate[X[[1]]] is Protected.".

Is there a way to plot using "dynamic" variables?

@Mr.Wizard It seems to me the underlying problem is that Evaluate should be placed outside the list, Evaluate@{X[[1]], 0, 1}. This is the issue in many posts, such as (5235) and (47907), and is also explained in this answer. I couldn't find one in which the issue was specifically using Evaluate in the second argument to Plot. It's usually the first argument. — Michael E2, Feb 07 '16 at 17:09
@MichaelE2 Yes, those are good, perhaps better, originals. And I found another related question and added it to my comment above. This question seems headed toward closure as "in the documentation" at this point; hopefully the links are useful to Markus and others. — Mr.Wizard, Feb 07 '16 at 17:14

m_goldberg · Accepted Answer · 2016-02-07T14:01:26.747

8

If you have a relatively recent version of Mathematica, you don't need to use Evaluate.

X = {Unique["x"]};
With[{x = X[[1]]}, Plot[Legended[2 x, x], {x, 0, 1}]]

edited Feb 07 '16 at 14:01

answered Feb 07 '16 at 13:41

m_goldberg

Using X={Unique["x"]};Plot[Legended[2 X[[1]], X[[1]]], {X[[1]], 0, 1}] does not work. I need something that works for symbol lists. – Markus Müller Feb 07 '16 at 13:45
1

@MarkusMüller Please edit your question to state clearly what you do need. – bbgodfrey Feb 07 '16 at 13:55
Sorry if my question was not clear. I fixed it. Basically, I am wondering how to plot a function which depends on "dynamic" variables created using Unique. – Markus Müller Feb 07 '16 at 14:00
With solves the problem. Thanks. – Markus Müller Feb 07 '16 at 14:02

1 Answers1