# Double script error on mathematical formula

The formula is printed correctly But I have this error for 6 times (I think it depends on the number of "f"):

Double subscript. ...al{f}\ped1\ped0+\mathnormal{f}\ped0\ped1}


I tried to look for a question to understand the error, but I could not find anything useful to understand the problem. Thanks in advance! Here the code

\noindent \textbf{Accuratezza del modello} = $\frac{\text{Numero di predizioni corrette}}{\text{Numero totale di predizioni}} = \frac{\mathnormal{f}\ped1\ped1+\mathnormal{f}\ped0\ped0}{\mathnormal{f}\ped1\ped1+\mathnormal{f}\ped0\ped0+\mathnormal{f}\ped1\ped0+\mathnormal{f}\ped0\ped1}$

• \frac{f_{11}+f_{00}}{f_{11}+f_{00}+f_{10}+f_{01}} Do you really think that \mathnormal{f} is necessary? – egreg Dec 18 '17 at 12:58

Such a formula should be displayed, to begin with; then \mathnormal is useless and \ped is a (wrong) command only defined for babel-italian and for text mode (LaTeX provides \textsubscript).

Math mode subscripts are introduced by _.

Do yourself a favor and forget about \ped and \ap.

$\textbf{Accuratezza del modello} = \frac{\text{Numero di predizioni corrette}} {\text{Numero totale di predizioni}} = \frac{f_{11}+f_{00}}{f_{11}+f_{00}+f_{10}+f_{01}}$


Better yet, use align*:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}

\usepackage{amsmath}

\begin{document}

Dimentica \verb|\ped| e \verb|\ap|; non avrebbero mai
dovuto essere definiti. Usa piuttosto la normale sintassi
\LaTeX{}
\begin{align*}
\textbf{Accuratezza del modello}
&= \frac{\text{Numero di predizioni corrette}}
{\text{Numero totale di predizioni}} \\
&=\frac{f_{11}+f_{00}}{f_{11}+f_{00}+f_{10}+f_{01}}
\end{align*}

\end{document} In math formulas you should use _ instead of \ped. (I guess that you use \usepackage[italian]{babel}.)

This should do the job for you:

\noindent \textbf{Accuratezza del modello} = $\frac{\text{Numero di predizioni corrette}}{\text{Numero totale di predizioni}} = \frac{\mathnormal{f}_{11}+\mathnormal{f}_{00}}{\mathnormal{f}_{11}+\mathnormal{f}_{00}+\mathnormal{f}_{10}+\mathnormal{f}_{01}}$