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MathGroup Archive 2001

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Re: Novice question regarding variable naming and subscripts

  • To: mathgroup at
  • Subject: [mg28188] Re: [mg28136] Novice question regarding variable naming and subscripts
  • From: Tomas Garza <tgarza01 at>
  • Date: Tue, 3 Apr 2001 02:38:06 -0400 (EDT)
  • References: <>
  • Sender: owner-wri-mathgroup at

Don't use "blank", i.e., the underscore "_", to "imply a subscript". It has
a well-defined mission in Mathematica. I suggest you use the basic input
palette to write F-subscript and it is much easier. Then (in input form) it

Subscript[F, i][F_] := F + a/2

and your plot will appear with

Plot[Evaluate[Subscript[F, i][F] /. a -> 1], {F, 0, 10}];

Copy this into your notebook, and convert the cells to StandardForm: select
each cell and then  Cell|ConvertTo|StandardForm so that the notation you
want to use shows properly.

Tomas Garza
Mexico City
----- Original Message -----
From: "William McHargue" <William at McHargue.Com>
To: mathgroup at
Subject: [mg28188] [mg28136] Novice question regarding variable naming and subscripts

> Hello to The Math Group,
> I am new to this group and have a burning question about Mathematica
> use. (I hope to give back to the group when I have something to
> contribute, but presently I'm still somewhat of a novice.)
> In some ways you could call me a "casual" user of Mathematica. I pick it
> up when a project demands, but often never get REALLY good at it.
> Typically I like to use it to both document and define a simulation or
> model. I would like to use the full 2D-input to define the various
> equations involved, but there seems to be a problem when I define, say,
> a function:
> F_i[F_]:=F+(a/2);
> (where "F_i" implies "F" subscript "i")
> Then I wish to, say, plot this function using a variable "F" (no
> subscript) using this:
> Plot[ F_i[F]/.a->1, {F, 0, 10}]
> When this is evaluated it says:
> Plot::"plnr" :  F_i[F]/.a->1 is not a machine-size real number at...
> (over and over again, and at valid values)
> Yet, it works fine if I pick a different independent variable. I realize
> I could use just "x" instead of "F", but by keeping the actual Input
> Form reading like the common equations in particular applications the
> whole thing is much easier to follow and debug.
> I wouldn't be surprised if I do not fully understand the way Mathematica
> manages its name space, but I would like subscripted names to be
> completely independent from their non-subscripted brothers--the way we
> humans might write equations and variables on paper.
> Any ideas, or perhaps chapters in the documenation I should dive into
> more deeply?
> Thanks in advance for any info in this regard,
> Bill.
> --
> William B. McHargue - Physicist
> <mailto:William at McHargue.Com>
> Yahoo/Jabber IM: William_McHargue

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