Adjust the exponent to switch between notations using siunitx

Question

I have a big question about the siunitx package and I hope somebody out there can help me.

At first I want to use the automatic number conversion of the package. So I defined:

\sisetup{scientific-notation = engineering}

But now every number is converted into the engineering format. For example: 0.01 => 10x10^3 But I want that this number is not converted automatically.

Is there an option to adjust, which tells the package at which max. Exponent number this conversion to scientific-notation should take place?

I have really a lot numbers in a paper and it would be really hard to put the scientific-notation on or off for each number manually.

Answer 1

I do not see anything in the documentation to control this behavior.

For the case where there are a few exceptions, you can manually switch it off for the ones you want with the \num[scientific-notation=false]{}.

Alternatively, if you can define exactly when you want the exponent to be added you can redefine the behavior of \num based on its value. Below I have defined \num to apply scientific-notation=false if

-\Threshold <= number <= \Threshold

where \Threshold is a value you define. With \Threshold=0.09 you get the results in the New column below for the value given in the Num column:

Notes:

• In the question it is suggested to use a maximum exponent to determine if scientific notation is to be used. I am not sure that such a solution is viable in general. Perhaps a solution based on the number of digits might work. Once a better algorithm is determined, the macro \IfLessThanOrEqual can be adjusted to suit.

Code:

Below I have adapted this solution from how to test if a number is negative to define \IfLessThanOrEqual:

\documentclass{article}
\usepackage{siunitx}
\usepackage{tikz}
\sisetup{scientific-notation = engineering}
\newcommand*{\Threshold}{0.09}%
\newcommand\IfLessThanOrEqual[4]{%
    \begingroup%
        \pgfmathsetmacro{\var}{abs(#1)-#2}%
        \pgfmathparse{ifthenelse(\var<=0,1,0)}%
        \ifdim\pgfmathresult pt= 1 pt%
                #3%
            \else%
                #4%
        \fi%
    \endgroup%
}%
\let\OldNum\num%
\renewcommand*{\num}[2][]{%
    \IfLessThanOrEqual{#2}{\Threshold}{%
        \OldNum[scientific-notation=false,#1]{#2}%
    }{%
        \OldNum[#1]{#2}%
    }%
}%
\begin{document}
\newcommand{\Row}[1]{#1 & \OldNum{#1} & \num{#1}}%
\begin{tabular}{l l l}
Num & Old & New\
\Row{0.01}\
\Row{0.09}\
\Row{0.091}\
\end{tabular}
\end{document}

Answer 2

The related question Scientific Notation Only For Large Numbers just got a perfect answer from Bruno le Floch, I supposed it would help to display it here as well.

The answer uses the package expl3 and defines a new command to test whether the number to be printed surpasses the threshold: \fpcmpTF.

\documentclass{article}
\usepackage{expl3,siunitx}
\sisetup{scientific-notation=true}
\ExplSyntaxOn
    \cs_new_eq:NN \fpcmpTF \fp_compare:nTF
\ExplSyntaxOff

\newcommand*{\ThresholdLow}{0.01} % Change to your taste
\newcommand*{\ThresholdHigh}{100}

\let\OldNum\num%
\renewcommand*{\num}[2][]{%
    \fpcmpTF{abs(#2)<=\ThresholdLow}{%
        \OldNum[scientific-notation=true,#1]{#2}%
    }{%
        \fpcmpTF{abs(#2)>=\ThresholdHigh}{%
            \OldNum[scientific-notation=true,#1]{#2}%
        }{%
            \OldNum[scientific-notation=false,#1]{#2}%
        }%
    }%
}%
\begin{document}
\newcommand{\Row}[1]{#1 & \OldNum{#1} & \num{#1}}%
\begin{tabular}{l l l}
Num & Old & New\\
\Row{0.01}\\
\Row{0.1}\\
\Row{1}\\
\Row{10}\\
\Row{100}\\
\end{tabular}
\end{document}

If you like this, then be sure to pass the vote to Bruno's answer at How to subtract both very large numbers and numbers smaller than one?.