As Yongjian Feng suggested, the expression can be written to a .txt file using the fprint function. First we have to create a LaTeX character array from a symbolic expression:
syms test
formula = latex(test); % This produces the output '\mathrm{test}'
LaTeX expressions in general contain commands which are denoted by a backslash. However, the function that is used to write strings to .txt file uses the backslah for formatting. Replacing the backslash with a double backslash solves this problem:
formula = strrep(formula, '\', '\\');
Finally, the character array can be written to the file:
fid = fopen('test_file.txt','wt');
fprintf(fid, formula);
fclose(fid);
