I have been trying to automate the production of stepped tables that contain conversion factors of all sorts. (See Protrusion of fractions in tabulars).
As part of this I have a rather convoluted macro to convert decimals to fractions. The algorithm works fairly well and sample output is shown below:
As I am trying to catch common fractions as those found in traditional units (1/12, 3/4, 1/60, 1/3 etc), I would like to be able to break out of the loop once a limit is reached. I have tested it using FPifgt
or similar but I am getting problems with the double fi
. Is there a way out of it?
The code is shown below (apologies for length):
\documentclass{article}
\usepackage{amsmath,fp}
\begin{document}
\makeatletter
\count@=1
\def\DecimalToFraction#1{
%helper macro
\FPset\zero{0}
\FPset\X{#1}
%% Set initial values
\FPadd\X{\X}{0.0000000001} % avoid overflows and divisions by zero
\FPset\Zi{\X}
\FPset\Di{1}
\FPset\Dprevious{0}
%% begin loop
\loop\ifnum\count@<13
%% numerator term
\FPtrunc\temp{\Zi}{0}
\FPsub\temp{\Zi}{\temp}
%% inverse
\FPdiv\Znext{1}{\temp}
%% Find Dnext
\FPtrunc\IntZnext{\Znext}{0}
%% Di x Int{Zi+1}
\FPmul\temp{\Di}{\IntZnext}
\FPadd\temp{\Di}{\Dprevious}
\FPset\Dnext{\temp}
\FPround\Dnext{\Dnext}{0}
%%% Find Ni+1
\FPmul\temp{\X}{\Dnext}
\FPround\temp{\temp}{0}
\FPset\Nnext{\temp}
\FPdiv\ratio{\Nnext}{\Dnext}
\(Z_i=\Znext\to \Nnext/\Dnext =\ratio\)
\FPset{\Dprevious}{\Dnext}
\FPset{\Di}{\Dprevious}
\FPset{\Zi}{\Znext}
\advance\count@ by1
\repeat
%% end of loop
\gdef\NUM{\Nnext}
\gdef\DEN{\Dnext}
\makeatother
}
\def\Test#1{%
\DecimalToFraction{#1}
The number $#1=\frac{\NUM}{\DEN}$
}
\Test{0.375}
\end{document}
Best Answer
To abort the loop after the current iteration simply
\let
the internal\iterate
macro to\relax
. If you want to skip the rest of the loop code you can use a macro defined to\fi\iffalse
for this (as Bruno already said).Abort at end of current iteration:
Abort immediately:
Explanation:
First lets look at the (LaTeX) definitions of
\loop
and\repeat
:As you see
\loop
stores everything between it and\repeat
into\iterate
which calls itself. This recursion implements the loop. The\expandafter
ensures that no dangling\fi
s get accumulated. As long the loop\if...
is true the text is executed, and\iterate
is called again after the\fi
. If the conditional is false everything until the\fi
is skipped including the\expandafter
. However if\iterate
is changed to\relax
the recursion stops independent of the conditional. Because this happens after the\fi
no cleanup is required.The
\breakloop
generates a\fi\iffalse
. The\fi
closes the loop conditional and the\iffalse
makes TeX skip everything until the final\fi
like the loop conditional would do.If you need to use FP conditionals inside the loop you have to make them "skip save" first. The problem is that FP define own
if
switches as macros which aren't recognized when TeX skips over an false path. To fix this define macros like thisThen use
\xFPiflt\x\y{<true>}{<false>}
instead of\FPiflt\x\y <true> \else <false> \fi
.