Why is there a decimal for 3x4=12.0?

Question

Why does \pgfmathresult display the result of 3x4 as 12.0?

\documentclass{article}

\usepackage{pgf}

\begin{document}

\pgfmathparse{3*4}
\pgfmathresult

\end{document}

This code yields a document whose sole contents is "12.0".

In some parts of the document I'm working on, I'll need decimal places, but not for grade 2 math.

How do I fix this?

\pgfmathparse{int(3*4)}. for more options, how to use pgfmath, see TikZ manual, part IV: Mathematical and Object-Oriented Engines. — Zarko, Sep 12 '16 at 23:53
In TikZ & PGF manual. Recent version is 3.0.1a. It is part of your package installation as file pgfmanual or you can find it on http://ctan.ijs.si/tex-archive/graphics/pgf/base/doc/pgfmanual.pdf — Zarko, Sep 13 '16 at 07:49
I still can't find it. Maybe I'm on the right pages, but see no relation to the number of decimal places. Would you mind letting me know the specific page numbers of the PDF I should be reading? — WeCanLearnAnything, Sep 15 '16 at 19:45
part IV: Mathematical and Object-Oriented Engines, pp. 921. math function are sumarised on pp. 928, in section 89.3 Syntax for Mathematical Expressions: Functions — Zarko, Sep 15 '16 at 21:01

cfr · Accepted Answer · 2016-09-13T10:13:02.270

15

First, you are not formatting the number when you say \pgfmathresult. Second, you have not specified any particular format for number printing. (Although the default format will do, in this case.)

Compare:

\documentclass{article}
\usepackage{pgf}
\begin{document}

\pgfmathparse{3*4}
\pgfmathresult

\pgfmathprintnumber\pgfmathresult

\pgfmathparse{int(3*4)}
\pgfmathresult

\pgfkeys{% just for example - doesn't actually matter here
  /pgf/number format/int detect,
}

\pgfmathparse{3*4}
\pgfmathprintnumber\pgfmathresult


\end{document}

PGF doesn't know you are typesetting Grade 2 maths rather than a doctoral dissertation in nuclear engineering!

edited Sep 13 '16 at 10:13

answered Sep 13 '16 at 00:00

cfr

198,882

Thanks! I used the \pgfmathparse{int(3*4)} option. I'll be starting a new thread for what I believe is a more complicated but related issue now. :) – WeCanLearnAnything Sep 13 '16 at 00:47
1

Not to quibble, but the integer representation "12" is far more likely to occur in a doctoral dissertation on number theory than the decimal/floating point representation "12.0". The latter is more likely in scholarly work dealing with applied math. – Deepak Sep 13 '16 at 10:11
@Deepak True. If such a dissertation includes any actual numbers at all, of course. – cfr Sep 13 '16 at 10:12
@cfr Also very true - lots of very high level math has practically no numbers in it! :) Although numbers would likely feature in a number theory paper, at least as coefficients. But papers on algebraic topology and the like will be dense in symbols, with numbers mainly featuring in the Lemmas and the references. – Deepak Sep 13 '16 at 10:13
@Deepak Will nuclear engineering do? – cfr Sep 13 '16 at 10:14
@cfr Sure! It was just a tongue-in-cheek comment anyway. :) – Deepak Sep 13 '16 at 10:15
@Deepak I knew it was a bad example when I wrote it, but it was late ... ;) – cfr Sep 13 '16 at 10:16

score 3 · Answer 2 · answered Sep 13 '16 at 10:25

The standard representation returned by PGF is with a decimal part, even if it is .0, due to how the internal work (it's TeX that adds .0 when requested to print the value of a \dimen register and PGF just strips the trailing pt), unless you declare the operation to return an integer.

An alternative is using expl3, whose floating point module adds a decimal part only if nonzero:

\documentclass{article}
\usepackage{expl3}

\ExplSyntaxOn
\cs_set_eq:NN \fpeval \fp_eval:n % get a user level version
\ExplSyntaxOff

\begin{document}

\fpeval{3*4}

\end{document}

Note you don't even need the double step of \pgfmathresult. The accuracy of the floating point module is according to IEEE standards, contrary to what PGF provides.

Try the following with PGF and you'll know what road to take.

\documentclass{article}
\usepackage{expl3,siunitx}

\ExplSyntaxOn
\cs_set_eq:NN \fpeval \fp_eval:n % get a user level version
\ExplSyntaxOff

\begin{document}

\fpeval{333*444}

\num[group-separator={\,}]{\fpeval{333*444}}

\num[group-separator={,}]{\fpeval{333*444}}

\end{document}

Why is there a decimal for 3x4=12.0?

2 Answers2