Symbolic toolbox: printing greek letters using latex() function

I use latex() function to print results of symbolic calculations and then paste results into a latex code. How do I make MatLab to add backslash in front of greek letters? Example:

syms xi a alpha

f = xi+a^alpha

latex(f)

This code produces output:

\mathrm{xi} + a^{\mathrm{alpha}}

What I want is to get a formula ready to paste into latex code (with backslashes in front of greek symbols):

\mathrm{\xi} + a^{\mathrm{\alpha}}

If it is not possible to do using Matlab, maybe there are other simple ways to automate the process of adding backslashes?

Thanks!

Answer 1

[Walter Roberson]

regexprep(f, '(alpha|beta|gamma|delta|epsilon|zeta|eta|theta|iota|kappa|lambda|mu|nu|xi|omicron|pi|rho|sigma|tau|upsilon|phi|chi|psi|omega)', '\\$1', 'preservecase')

[Anton]

Awesome! Thank you!

[Svyatoslav Kharitonov]

Dear all,

I have tested function latex in MATLAB R2017b, and got quite confusing results.

The code:

alpha = sym('alpha');
beta = sym('beta');
psi = sym('psi');
omega = sym('omega');
latex(alpha)
latex(beta)
latex(psi)
latex(omega)

And results:

ans =

      '\alpha '

ans =

      '\mathrm{beta}'

ans =

      '\mathrm{psi}'

ans =

      '\omega '

Does someone know, where this difference of interpretation of greek letters comes from?

Thank you in advance!

[Walter Roberson]

Svyatoslav Kharitonov:

Interesting. Good question. I would call that a bug. If \mathrm is to be used then it would have to be \mathrm{\beta} not \mathrm{beta}

There turns out to be two expression to tex conversion routines in MuPAD (the symbolic engine.) One of them, them one seemingly called by latex(), is symobj::TeX, which invokes generate::TeX:inner with SimplifiedIdentifierRules set to true. The other one, the documented one, is generate::TeX which calls generate::TeX::inner with SimplifiedIdentifierRules set to false.

Now, called from the MATLAB level through the mupadmex() call, both of those routines produce the same answer, the \mathrm{beta} answer. But if you open a MuPAD notebook and execute at that level, then symobj::TeX returns \beta (which is valid) and generate::TeX returns \mathrm{beta} (which is not.) The interface to the symbolic engine is messing up the call.

Checking further, I see that if you directly feval(symengine,'symobj::TeX', 'beta') then you get the \beta result, but feval(symengine,'generate::TeX', sym('beta')) gets back the bogus \mathrm{beta} . This has to do with the deep details of the interface between the MATLAB level and the symbolic engine.

At the moment, the workaround seems to be to change

latex(SYMBOLIC_EXPRESSION)

to

sprintf(char(feval(symengine,'symobj::TeX', char(SYMBOLIC_EXPRESSION))))

... Or, much more simply, use a routine I had never heard of before but which has existed for a long time: https://www.mathworks.com/help/matlab/ref/texlabel.html

texlabel(SYMBOLIC_EXPRESSION)

I do not know how well this will work with more complicated expressions -- it appears it will use a more straight-forward conversion and less mathematical, such as {A}/{B} instead of \frac{A}{B}

I just filed a bug report on this.