I wonder why \mathcal{f} is not working but \mathcall{f} does (the print looks fine), even with the undefinedcontrolsequence error. This happens inside the equation mode and inside the text.`

 U_{TT} = A e^{-bR} - \sum_{n=3}^5 \mathcall{f}_{2n} (bR) \frac{C_{2n}}{R^{2n}}

..in which $\mathcall{f}_{2n}(R)$ are the damping functions from eq. (98).

closed as off-topic by egreg, Steven B. Segletes, Mensch, zeroth, Mico Sep 2 '16 at 14:49

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    Notice the difference in argument delimiter: parens () are not the standard LaTeX delimiter (the case that doesn't work), but braces {} are (the example that works). – Steven B. Segletes Sep 2 '16 at 14:04
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    The command is \mathcal with a single ell. On the other hand, \mathcal{f} is wrong to begin with, because \mathcal only applies to uppercase letters. – egreg Sep 2 '16 at 14:05
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    I'm voting to close this question as off-topic because the issue is due to a typo – egreg Sep 2 '16 at 14:05
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    I'm not sure what you're expecting. (1) \mathcall is undefined (2) \mathcal (this is the correct name) only makes sense with uppercase letters, such as \mathcal{F} (3) \mathcal(f) tries to apply \mathcal to ( and the result will be unpredictable (4) \mathcal{f} will only print random rubbish (maybe an f) – egreg Sep 2 '16 at 14:10
  • Sorry, yes, in both cases I write {}. The issue is that for the correct command: "\mathcal{f}", the pring goes as: "{", and the undefined control sequence error doesn't appear. Strangely, with "\mathcall{f}", the print is fine.. and the error shows, lots of them by now with the same typing. – Vals Sep 2 '16 at 14:29

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