Does PlotLegends not work in MM 11?

Question

I literally just downloaded MMA11 and upgraded from MMA 10.4, and PlotLegends seems to not work the way it did previously... Kind of annoying. Anyone knows why?

 Clear[var, expr, blah, g, derivatives];
 var = Input["Type a variable, such as x, in this window."];
 expr = Input["Type an expression to be differentiated in the variable you just typed in the last window."];
 g[blah_] = expr /. {var -> blah};
 derivatives := {g[var], g'[var]}
 Plot[{derivatives}, {x, -3, 5}, {PlotLegends -> "Expressions", 
 PlotLabel -> "A function and its Derivative", PlotRange -> 10}]

Do you have a more minimal example demonstrating this that doesn't reply on Input statements? — ktm, Nov 04 '16 at 18:46
Try changing Plot[{derivatives},...] into Plot[Evaluate@derivatives,...] — corey979, Nov 04 '16 at 18:49
It works PERFECTLY fine on 10.3.. I have both versions and just ran the same exact code. — Brandon, Nov 04 '16 at 18:50
@corey979 ok that fixes it... is that not a bug?? why would it work that well in 10.3 but then in 11 it doesn't work — Brandon, Nov 04 '16 at 18:52
Your code (without Evaluate) doesn't work for me on v10.4.1. // It's not a bug, it's a normal behaviour. — corey979, Nov 04 '16 at 18:53

score 7 · Accepted Answer · edited Apr 13 '17 at 12:55

First of all, this is not a bug in PlotLegends. You can tell because the plot itself is using the color for a single data set, implying that it thinks there is only one multi-valued function present. Since PlotLegends with "Expressions" or Automatic is sensitive to the number of functions, they will not display a legend when only one is present. The issue is then with how Plot is interpreting derivatives.

After a little experimentation, it comes down to the use of SetDelayed vs Set. When Set is used to define the variable,

d1 = {Sin[x], Cos[x]}
Plot[d1, {x, 0, 2 Pi}]

the expected image is produced.

But, when SetDelayed is used,

d2 := {Sin[x], Cos[x]}
Plot[d2, {x, 0, 2 Pi}]

it does not. There was some work on the parser between 10.3 and 10.4 which is likely causing this change in behavior, but I am not inclined to consider this a bug. Simply, with SetDelayed the function is expected to be evaluated over and over again, and should be thought of as the equivalent of using

f[x_] := {Sin[x], Cos[x]}
Plot[f[x], {x, 0, 2 Pi}]

which generates a plot identical to d2.

Correction: after looking at this again, and actually running this with PlotLegends with Set being used shows the same behavior. Therefor, I would say it is a bug.

I have the same problem - does anyone have a fix? – Howard Lovatt Apr 04 '18 at 23:30 — Howard Lovatt, Apr 04 '18 at 23:30

score 0 · Answer 2 · answered Apr 04 '18 at 23:36

0

If you add Evaluate to the expression to be plotted there it works. Must be some bug in Plot.

answered Apr 04 '18 at 23:36

Howard Lovatt

151
2

Does PlotLegends not work in MM 11?

2 Answers2