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MathGroup Archive 2004

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Re: symbol replace

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51244] Re: [mg51241] symbol replace
  • From: "Maxim A. Dubinnyi" <maxim at nmr.ru>
  • Date: Sun, 10 Oct 2004 01:57:15 -0400 (EDT)
  • References: <200410090819.EAA09741@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Answer to the first question.
You should temporary replace \!\(E\_0\) (Subscript[E,0]) with "E0" or
other unused symbol, then perform substitution and finally replace "E0" 
back:

In[1]=  E*Subscript[E,0]/.
          Subscript[E,0]->"E0"/.
          E->Subscript[E,0]/.
          "E0"->Subscript[E, 0]
Out[1]= Subscript[E, 0]^2

The following is general solution for this problem.
Function "SubscriptProtectReplaceAll" is the same as
Build-In function "ReplaceAll", but it preserves parts of
Subscripted symbols from replacing:

In[2]=  SubscriptProtectReplaceAll[exprn_, rules_] :=
          Module[{ProtectRules},
            ProtectRules =
              Cases[
                exprn,
                Subscript[A_,b_]:>(Subscript[A,b]->Unique[tmp]),
                {0, Infinity},
                Heads->True
              ];
            exprn/.ProtectRules/.rules/.(Reverse/@ProtectRules)
          ]

In[3]=  SubscriptProtectReplaceAll[
          E*Subscript[E,0],
          E->Subscript[E,0]
        ]
Out[3]= Subscript[E,0]^2;

More sophisticated example:

In[4]=  \!\(SubscriptProtectReplaceAll[A+A\_2+A\_A+A\_\(A\_3\)+A\_4[x],
            A->A\_1]\)
Out[4]= \!\(A\_1+A\_2+A\_A+A\_\(A\_3\)+A\_4[x]\)

The following code permanently substitutes "ReplaceAll" with 
"SubscriptProtectReplaceAll":

In[5]=  Unprotect[ReplaceAll];
        SubscriptProtect[ReplaceAll]=True;
        (exprn_ /. rules_)/;SubscriptProtect[ReplaceAll]:=
          Block[{SubscriptProtect},
            SubscriptProtect[ReplaceAll]=False;
            SubscriptProtectReplaceAll[exprn, rules]
          ];
        Protect[ReplaceAll];

Now you can use ordinary substitution symbol "/.":

In[6]=  \!\(A+A\_2+A\_A+A\_\(A\_3\)+A\_4[x]/.A->A\_1\)
Out[6]= \!\(A\_1+A\_2+A\_A+A\_\(A\_3\)+A\_4[x]\)

Resetting

In[7]=  SubscriptProtect[ReplaceAll]=False;

Will return you to ordinary substitution rules.



Sincerely,
Maxim A. Dubinnyi



symbio wrote:

>I am facing 2 problems with Mathematica:
> 1st problem)
>With replace all command,  when I use it with subscripts I get an unintended 
>effect, this is what I do:
>E * (Eo) /. E -> (Eo)
>I intend to replace only E with Eo, but Mathematica instead replaces all E's 
>with (Eo) and I get this instead:
>(Eo) * (Eo)o
>Please note the 'o' in Eo is supposed to be a subscript here and reads Enot. 
>Can anyone please help?
>here is the Mathematica code:
>
>In[1]:=
>\!\(E\ *\ E\_0\ /. \ E -> \ E\_0\)
>Out[1]=
>\!\(\[ExponentialE]\_0\ \((\[ExponentialE]\_0)\)\_0\)
>
>2nd problem)
>I like to use descriptive names for my variables with Underscore to separate 
>the names, it's really easier to read, but of course underscore is a special 
>character in Mathematica unfortunately, so is there an alternative??   For 
>example, I like to use variable Dynamic_Energy_of_Stars_With_Sand = 123;  Is 
>there something else equally as obvious as Underscore that maybe used for 
>purpose of separting words in a variables names??
>
>Thanks a lot for your help 
>
>  
>



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