# Converting numbers to scientific notations

I have some numbers output from Matlab and I want to show them as tables in LaTeX. The numbers are in the form 0.14190949656253118000 or 0.01234e-3 and I want to show them in scientific notation. How can I find/write, a macro that is called like \scn{0.14190949656253118000} or \scn{0.01234e-3} and results in $1.41x10^{-1}$ or $1.23x10^{-5}$. Note that the number of digits after the decimal points should be configable.

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\documentclass{article}
\usepackage[scientific-notation=true]{siunitx}
\listfiles
\begin{document}

%\num{0.14190949656253118000}
\num{0.1419094965}

\end{document}


However, for your particular number, siunitx versions lower than 2.4n return a "number too big" error unless you round the number off (as you had originally indicated, but I forgot about). That prompted me to write the following MATLAB function that will print the LaTeX code for your numbers to whatever precision you want:

function s=pp(x,n)
% pretty-print a value in scientific notation
% usage: s=pp(x,n)
% where: x a floating-point value
%        n is the number of decimal places desired
%        s is the string representation of x with n decimal places, and
%          exponent k
exponent=floor(log10(abs(x))); %to accomodate for negative values
mantissa=x/(10^exponent);
s=sprintf('$%*.*f \\times 10^{%d}$',n+3,n,mantissa,exponent);
% returns something like '$1.42 \times 10^{-1}$'


Examples:

>> s1=pp(0.14190949656253118000,2)
s1 =
$1.42 \times 10^{-1}$
>> s2=pp(0.01234e-3,3)
s2 =
$1.234 \times 10^{-5}$


But again, any recent version of siunitx and Boris' answer will work fine for rounded numbers, and siunitx 2.4n will work fine even without rounding.

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Which version of siunitx do you have? You should not get the 'too big' error with the latest release. – Joseph Wright Apr 4 '12 at 7:29
I'll update and check again. – Mike Renfro Apr 4 '12 at 11:52
Updated from CTAN, got siunitx 2.4l, same problem. Updating answer with new details. – Mike Renfro Apr 4 '12 at 12:52
Ah, that's not quite what I tried :-) The question indicates that the output should be rounded (which was where there used to be a bug with the number of digits in the mantissa!). So I both rounded and forced scientific notation, which works fine. I will investigate this other issue when I get a moment. – Joseph Wright Apr 4 '12 at 12:59
Yep. Forgot the rounding, which Boris remembered to include. – Mike Renfro Apr 4 '12 at 13:20

The macro \num from, e.g. siunitx does just this. For example

\documentclass{article}
\pagestyle{empty}
\usepackage{siunitx}
\begin{document}
\num[round-precision=2,round-mode=figures]{0.1419094};
\num[round-precision=2,round-mode=figures,
scientific-notation=true]{0.1419094};
\num[round-precision=2,round-mode=figures,
scientific-notation=true]{0.1419094e-6};
\num[round-precision=2,round-mode=figures,
scientific-notation=engineering]{0.1419094e-6}
\end{document}


Note that too many digits in the input may lead to error "Number is too big".

Also, the optional arguments in \num can be set for all numbers using \sisetup.

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It would be better to show a complete example. By default \num{0.14190949656253118000} produces 0.141 909 496 562 531 180 00} – Peter Grill Apr 4 '12 at 0:47
ok, added some examples – Boris Apr 4 '12 at 1:43
Thanks Boris, I just defined a macro like this \newcommand{\sn}[1]{\num[round-precision=2,round-mode=figures,scientific-notati‌​on=true]{#1}} since I want to make the numbers consistent throughout the document. – Helium Apr 4 '12 at 2:39
easier to say \sisetup{round-precision=2,round-mode=figures,scientific-notation=true}, and then just user \num. – Boris Apr 4 '12 at 3:03