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Superscripts can be included in axis labels by the use of the caret symbol (e.g., Plot[x^2, {x, -1, 1}, AxesLabel -> {x, x^2}]).

How does one include subscripts in an axis label? The use of the underscore character does not seem to work (e.g., Plot[f, {x, -1, 1}, AxesLabel -> {x, f_i(x)}]).

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4 Answers 4

up vote 10 down vote accepted

There is a subtle problem if you use strings as axis labels. Look closely at a plot like this:

Plot[f, {x, -1, 1}, AxesLabel -> {x, "\!\(\*SubscriptBox[\(f\), \(i\)]\)(x)"}]

You will see that the argument x in the function appears in a different font style than the argument on the horizontal axis.

To make sure that you get a consistent font style on both axes using the default styling for graphics, you should use the following:

Plot[f, {x, -1, 1}, AxesLabel -> {x, HoldForm[Subscript[f, i][x]]}]

Of course, to enter the Subscript expression in your label, you can still use the keyboard shortcuts that are mentioned by @Szabolcs.

The argument in HoldForm is your vertical label, typed in actual Mathematica syntax with square brackets for the function argument. I didn't surround the horizontal label in HoldForm, but you could do that for safety, in particular if your variable x has been assigned a value somewhere else in the Notebook.

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Thanks, that ensures consistent typesetting of the axis labels. In my case, variables in the axis labels remain italicized. –  user001 Mar 15 '12 at 18:59
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Yes, it's TraditionalForm. –  Jens Mar 15 '12 at 19:01
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Enclose the label in quotation marks for safety (just in case any symbols you use in them are defined), and enter two-dimensional input. Check the documentation on how to do it. You can enter a subscript using Ctrl-_ or Ctrl--. The Basic Math Assistant palette can be useful as well---it has a Typesetting section.

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oooh, how do you do the nice CTRL commands? –  tkott Mar 15 '12 at 18:44
    
@tkott Click the edit link to see ;-) It was really useful here because CTRL-- isn't very clear... Maybe CTRL-[-] –  Szabolcs Mar 15 '12 at 18:44
    
smacks head thanks :) –  tkott Mar 15 '12 at 18:45
    
Despite the fact than I ran out of votes hours ago I keep trying to vote. It's become a habit. –  Mr.Wizard Mar 15 '12 at 18:46
    
Thanks. When I enclose the label in quotation marks, it romanizes the text. Can I force it to remain italic? If I try LabelStyle->{Italic}, the tick labels are italicized in addition to the axis labels. I prefer for the axis labels to be italic and the tick labels to be roman. –  user001 Mar 15 '12 at 18:55
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That's because _ is only a subscript in LaTeX world. In MMA, you can simply use CTRL+-. The following should show you what I mean (once you copy it into MMA):

Plot[Sin[x], {x, -1, 1}, 
 AxesLabel -> {x, "\!\(\*SubscriptBox[\(f\), \(i\)]\)[x]"}]

Note that the reason that x^2 shows up like it does is because ^2 is automatically changed to MMA's boxes / display format. If you were to write:

Plot[Sin[x], {x, -1, 1}, AxesLabel -> {x, "x^2"}]

You'll notice the caret stick around.

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Thanks, I erroneously tend to assume I can transplant LaTeX practices to Mathematica. –  user001 Mar 15 '12 at 18:53
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Another option is to create the label with strings:

Plot[f, {x, -1, 1},
 AxesLabel -> {x, 
   Style[Row[{Subscript["f", "i"], "(x)"}], FontFamily -> "Times", 12,
     Italic]}]
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This works fine in most simply labels, but it quickly gets ugly when you have actual Mathematica expressions as labels. Just replace the vertical label by Sin[x] and ask how you'd format that in a string so that it doesn't come out as sin(x) but sin(x). This is just a simple example - the point is that it's much better to let the default TraditionalForm in plot labels do the work for you. –  Jens Mar 15 '12 at 21:02
    
I agree @Jens but the question related to a simple subscript. –  Mike Honeychurch Mar 15 '12 at 21:04
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