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I would ideally like to not have to spend a lot of time writing LaTeX for complicated algebraic expressions that I've worked out in Mathematica. I know that I can "copy-as-LaTeX", but my current issue is that my algebraic expressions are often formatted slightly wrong.

(Additionally, any general tips for working between $ \mathrm\LaTeX $ and Mathematica would be appreciated!)

EDIT: Explicitly showing the code: 

expression = -p12 β - 1/2 I (2 p12 (Δc - Δp) - p42 Ωa + p13 Ωc - p32 Ωp + p14 Ωs)

For example for the following algebraic expression:

I would like it to be sorted by variables in the following order (p12, p13, p14, p32, p42):

To look like:

$ (-\beta - i (\text{$\Delta $c}-\text{$\Delta $p}))\text{p12}+\text{$\Omega $c} \text{p13} +\text{$\Omega $s} \text{p14} - \text{$\Omega $p} \text{p32}-\text{$\Omega $a} \text{p42} $

If I use this code:

Collect[expression, {p12, p13, p14, p32, p42}]

it doesn't seem to organize the variables in this order (of {p12, p13, p14, p32, p42}). instead, it returns an ordering:

enter image description here

Additionally...I've observed that if I copy-as latex, what is above appears. But if I look at what I am copying, it has this form:

$\text{p12} (-\beta +i (\text{$\Delta $p}-\text{$\Delta $c}))-\frac{i \text{p13} \text{$\Omega $c}}{2}-\frac{i \text{p14} \text{$\Omega $s}}{2}+\frac{i \text{p32} \text{$\Omega $p}}{2}+\frac{i \text{p42} \text{$\Omega $a}}{2}$

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  • $\begingroup$ Could you give an example of how Collect gives the "wrong" parsing of an equation? $\endgroup$
    – David G. Stork
    Mar 7, 2020 at 2:48
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    $\begingroup$ Plus is Orderless $\endgroup$
    – Michael E2
    Mar 7, 2020 at 3:01
  • $\begingroup$ @DavidG.Stork, I added the example for me, but it's a bit strange. What I see it returning as an output appears to be sorted incorrectly, but when I copy it as latex, it actually gives me the correct order! $\endgroup$
    – Steven Sagona
    Mar 7, 2020 at 3:16
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    $\begingroup$ People here generally like users to post code as Mathematica code instead of just images or TeX, so they can copy-paste it. It makes it convenient for them and more likely you will get someone to help you. You may find this meta Q&A helpful $\endgroup$
    – Michael E2
    Mar 7, 2020 at 3:32
  • $\begingroup$ I added code that can be copy-pasted. $\endgroup$
    – Steven Sagona
    Mar 7, 2020 at 7:47

2 Answers 2

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As is mentioned in the comment, Plus is orderless. To solve this problem, one may replace Plus by another function, say plus, and define the format for plus. For example,

Format[plus[x__]]:=HoldForm[Plus[x]]; var={p12, p13, p14, p32, p42}; SortBy[plus@@Collect[expression,var],Cases[#,Alternatives@@var,{0,Infinity}]&]//TeXForm

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$\begingroup$

Perhaps this:

MonomialList[expression, 
     {p12, p13, p14, p32, p42}] /. 
   {args__} :> HoldForm[Plus[args]]

enter image description here

TraditionalForm[expression] shows the monomials in the same order, but I think it's merely a coincidence.

You have to hold Plus to keep the arguments from being reordered, just as @Wen Chern has done, too. This sort of manipulation is usually only done for the purposes of presenting output in a more human-readable form. It is not usually a convenient way to compute with expressions.

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  • $\begingroup$ Thanks. I also need the variables to be to the right of the coefficients. Is that also doable? $\endgroup$
    – Steven Sagona
    Mar 9, 2020 at 19:11

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