Ordering of monomial terms

Question

I have monomials with variables $a_1,\, a_2,\,\dots$ also their complex conjugates. I found that their order within the monomial depends on at which point I set the overline for the complex conjugate. It was impossible to order them by their index (i.e., have $a_1$ and $\bar a_1$ close together).

But now I added coefficients for the monomial terms and, because they are greek letters, they will be sorted to the end of the monomial. What causes/influences this ordering? How can I get them placed at the beginning?

Here's code for two monomials, both as LaTeX and input, showing what I am experiencing.

$\qquad \left\{a_1 \beta _1 S_{i_1},\,a_3 a_6 \beta _2 \overline{a_4} \right\}$

{Subscript[β, 1]*Subscript[a, 1]*Subscript[S, Subscript[i, 1]], 
 OverBar[Subscript[a, 4]]*Subscript[β, 2]*Subscript[a, 3]*Subscript[a, 6]}

score 1 · Accepted Answer · edited Apr 13 '17 at 12:56

I found How do I reassign canonical ordering of symbols? and adapted Simon Woods answer to my problem. The following does the trick:

reorderSymbols[expr_, symbols_List] := With[{s = symbols}, 
  HoldForm[Evaluate[expr /. Thread[s -> Sort@s]]] /. Thread[Sort@s -> s]]

reorderPoly[poly_] := Module[{ss},
  mapC[c_] := Map[(Subscript[c, #1])&,Range[Length[poly]]];
  ss = Flatten[Map[mapC,{\[Alpha],\[Beta],\[Gamma],\[Delta],\[CurlyEpsilon],\[Zeta]}]]~Join~Map[(Subscript[a, #])&,Range[6]]~Join~Map[(
  \!\(\*OverscriptBox[
  SubscriptBox[\(a\), \(#\)], \(_\)]\))&,Range[6]];
  reorderSymbols[poly, ss]
]

reorderPoly[{Subscript[β, 1]*Subscript[a, 1]*Subscript[S, Subscript[i, 1]], 
  OverBar[Subscript[a, 4]]*Subscript[β, 2]*Subscript[a, 3]*Subscript[a, 6]}]

Ordering of monomial terms

1 Answers1