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Re: Need just enough underbars

  • To: mathgroup at
  • Subject: [mg18346] Re: Need just enough underbars
  • From: dreiss at (David Reiss)
  • Date: Wed, 30 Jun 1999 14:13:18 -0400
  • Organization: Scientific Arts
  • References: <7l5sf2$>
  • Sender: owner-wri-mathgroup at

In article <7l5sf2$ih2 at>, Patrick Reany <reany at> wrote:

> I'm trying to use underbars to distinguish new variables from old in a
> differential eqn of state under a change of independent variables. I
> want all upper case letters to have an underbar in the new form. Some
> already have the underbar while others do not. How do I add the
> underbars to the ones that do not have them while not adding another
> underbar to the ones that already do. Below is an example form derived
> by using FullForm[]:
> Equal[Plus[Times[j,P],HoldForm[D[UnderBar[T],UnderBar[P]]],
>     Times[-1,T,HoldForm[D[UnderBar[V],UnderBar[U]]]]],0]
> where one 'P' and one 'T' need to have the underbar added.
> Thanks
> Patrick

Here is one quick way that I just hacked together as 
fast as possible.  First I deconstruct the expression 
by removing the underbars (assuming that the only 
quantities that have underbars are capital letters --
if this isn't true then you hahave to do a bit more), 
then I put them back but take care to only do this with symbols
defined in the Global' context:

j*P + HoldForm[D[UnderBar[T], UnderBar[P]]] - 
    T*HoldForm[D[UnderBar[V], UnderBar[U]]] /. 
   UnderBar[x_] :> x /. 
  (z_)?(UpperCaseQ[ToString[#1]] && Context[#1] === 
       "Global`" & ) :> UnderBar[z]

Perhaps there are much more elegant ways of doing this...



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