How can I control 'TraditionalForm' substitutions and formatting in special cases?

Question

eqns = TraditionalForm[HoldForm[Subscript[W, #][#] = ρ^s[#] Subscript[ω, #] ρ^-s[#]],] & /@ Range[4]

which (with eqns//TableForm) give me

$$ W_1(1)=\rho ^{s(1)} \omega _1 \rho ^{-s(1)}\\ W_2(2)=\rho ^{s(2)} \omega _2 \rho ^{-s(2)}\\ W_3(3)=\rho ^{s(3)} \omega _3 \rho ^{-s(3)}\\ W_4(4)=\rho ^{s(4)} \omega _4 \rho ^{-s(4)} $$

as I expect. But I need to substitute evaluations of s for various argument values. When I do this, for many values of s I get what I expect; but for others, I'm failing the get substitutions I need, or get odd reformatting that I don't expect. For example if s[#]& /@ {1,2,3,4} happens to be {0,23,10,-1}, I get

$$ W_1(1)=\rho ^0 \omega _1 \rho ^0\\ W_2(2)=\rho ^{23} \omega _2 \rho ^{-23}\\ W_3(3)=\rho ^{10} \omega _3 \rho ^{-10}\\ W_4=\frac{\rho ^{-(-1)} \omega _4}{\rho } $$

when what I need is

$$ W_1(1)=\omega _1\\ W_2(2)=\rho ^{23} \omega _2 \rho ^{-23}\\ W_3(3)=\rho ^{10} \omega _3 \rho ^{-10}\\ W_2(2)=\rho ^{-1} \omega _2 \rho ^{1}\\ $$

How can I get Mathematica the make the correct substitutions?

Much worse, Mathematica does not correctly copy any of these expressions as LaTeX. — orome, Mar 09 '15 at 16:30

score 1 · Answer 1 · answered Mar 09 '15 at 18:45

formatter[fab_, c_] := Block[{p1, p2, lhs, rhs, fn},
  rhs = If[fab == 0, Subscript[\[Omega], c], 
  If[fab < 0, fn = Abs[fab]; 
  HoldForm[\[Rho]^-f Subscript[\[Omega], c] \[Rho]^f] /. f -> fn, 
  HoldForm[\[Rho]^fab Subscript[\[Omega], c] \[Rho]^-fab]]];
  lhs = Subscript[W, fab][c];
  Replace[Evaluate[{lhs, rhs}], 
  List[a__, b__] :> HoldForm[Set[a , b]], Heads -> True]]

And then

 formatter[0,2]

or

formatter[-1,2]

etc.

Of course you can use formatter[-1,2]//TeXForm or //TraditionalForm if so desired.

score 1 · Answer 2 · answered Mar 11 '15 at 00:00

Since you want Mathematica to perform some simplifications of your expression, I don't think this is purely formatting question.

Inferring from your desired simplifications of $\rho^i\omega\rho^{-i}$ for different $i$, it is supposed to be some form of multiplication, but different than built-in Times function.

I would start with defining desired properties of your multiplication. To get results from examples in question this should be enough:

ClearAll[myTimes]
myTimes[l___, 1, r___] := myTimes[l, r]
(* To make it more similar to multiplication, you could add something like: *)
(*myTimes[___,0,___]=0;
myTimes[l___,x_,x_,r___]:=myTimes[l,x^2,r]
myTimes[x_]:=x
myTimes[]=1;
SetAttributes[myTimes,{Flat,OneIdentity}]*)
(* but this is not needed for examples from question. *)

Now let's assign desired formatting to myTimes function:

ClearAll[toPowerBoxes];
SetAttributes[toPowerBoxes, HoldAllComplete]
toPowerBoxes[{expr___}, form_] :=
    List @@ Replace[
        HoldComplete[expr],
        {
            Power[x_, y_] :> SuperscriptBox[MakeBoxes[x, form], MakeBoxes[y, form]], 
            x_ :> MakeBoxes[x, form]
        },
        {1}
    ]
MakeBoxes[HoldPattern@myTimes[expr__], StandardForm] ^:=
    RowBox[{"myTimes", "[", RowBox[Riffle[toPowerBoxes[{expr}, StandardForm], ","]], "]"}]
MakeBoxes[HoldPattern@myTimes[expr__], TraditionalForm] ^:=
    With[{boxes = RowBox[toPowerBoxes[{expr}, TraditionalForm]]},
        InterpretationBox[boxes, myTimes[expr]]
    ]

Examples from question, with unevaluated s:

Subscript[W, #][#] == myTimes[ρ^s[#] , Subscript[ω, #], ρ^-s[#]] & /@ Range[4]
% // TableForm // TraditionalForm

$\{W_1[1] == \text{myTimes}[\rho^{s[1]}, \omega_1, \rho^{-s[1]}], ...\}$

(*Out[]//TraditionalForm=*)

$W_1(1)=\rho ^{s(1)}\omega _1\rho ^{-s(1)} \\ ...$

and when s evaluates to something:

Block[{s},
    s[1] = 0; s[2] = 23; s[3] = 10; s[4] = -1;
    Subscript[W, #][#] == myTimes[ρ^s[#] , Subscript[ω, #], ρ^-s[#]] & /@ Range[4]
]
% // TableForm // TraditionalForm
% // TableForm // TeXForm

$\{ W_1[1] == \text{myTimes}[\omega_1], W_2[2] == \text{myTimes}[\rho^{23}, \omega_2, \rho^{-23}], W_3[3] == \text{myTimes}[\rho^{10}, \omega_3, \rho^{-10}], W_4[4] == \text{myTimes}[\rho^{-1}, \omega_4, \rho] \}$

(*Out[]//TraditionalForm=*)

$W_1(1)=\omega _1 \\ W_2(2)=\rho ^{23}\omega _2\rho ^{-23} \\ W_3(3)=\rho ^{10}\omega _3\rho ^{-10} \\ W_4(4)=\rho ^{-1}\omega _4\rho$

(*Out[]//TeXForm=
\begin{array}{c}
 W_1(1)=\omega _1 \\
 W_2(2)=\rho ^{23}\omega _2\rho ^{-23} \\
 W_3(3)=\rho ^{10}\omega _3\rho ^{-10} \\
 W_4(4)=\rho ^{-1}\omega _4\rho  \\
\end{array}*)

You can also select StandardForm expression containing myTimes and use Copy As > LaTeX. Result is the same as output of TeXForm.

How can I control 'TraditionalForm' substitutions and formatting in special cases?

2 Answers2

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