Pgfmathresult approximation?

Question

I need to do some simple calculations like these:

\documentclass[a4paper,10pt]{article}
\usepackage{tikz}
\begin{document}
\pgfmathparse{1*0.4}\pgfmathresult 

\pgfmathparse{2*0.4}\pgfmathresult

\pgfmathparse{3*0.4}\pgfmathresult

\pgfmathparse{4*0.4}\pgfmathresult 

\pgfmathparse{5*0.4}\pgfmathresult

\pgfmathparse{15*0.4}\pgfmathresult
\end{document}

etc, Say I need to do this for all the numbers between 1 and 60.

How do I get the correct results? Actually the only one that works is the first mathparse, in the remaining cases I got strange numbers.

Answer 1

TeX is not really good at floating-point work: there are however several implementations that are available. A few examples. First, you could active the TikZ FPU code:

\documentclass[a4paper,10pt]{article}
\usepackage{tikz}
\usetikzlibrary{fpu}
\pgfkeys{/pgf/fpu,/pgf/fpu/output format=fixed}
\begin{document}
\pgfmathparse{1*0.4}\pgfmathresult 

\pgfmathparse{2*0.4}\pgfmathresult

\pgfmathparse{3*0.4}\pgfmathresult

\pgfmathparse{4*0.4}\pgfmathresult 

\pgfmathparse{5*0.4}\pgfmathresult

\pgfmathparse{15*0.4}\pgfmathresult
\end{document}

or again with TikZ you could use the fixed point code in fp:

\documentclass[a4paper,10pt]{article}
\usepackage{fp,tikz}
\usetikzlibrary{fixedpointarithmetic}
\pgfkeys{/pgf/fixed point arithmetic}
\begin{document}
\pgfmathparse{1*0.4}\pgfmathresult 

\pgfmathparse{2*0.4}\pgfmathresult

\pgfmathparse{3*0.4}\pgfmathresult

\pgfmathparse{4*0.4}\pgfmathresult 

\pgfmathparse{5*0.4}\pgfmathresult

\pgfmathparse{15*0.4}\pgfmathresult
\end{document}

Alternatively, you could use the LaTeX3 FPU:

\documentclass[a4paper,10pt]{article}
\usepackage{expl3}
\ExplSyntaxOn
  \cs_set_eq:NN \fpeval \fp_eval:n
\ExplSyntaxOff
\begin{document}
\fpeval{1*0.4} 

\fpeval{2*0.4}

\fpeval{3*0.4}

\fpeval{4*0.4} 

\fpeval{5*0.4}

\fpeval{15*0.4}
\end{document}