Component Library and automatic calculations with FPeval

Question

I have come upon a problem I'd like to solve but unable to by myself. My intention is to create a library of components with different parameters and do calculations with FPeval. Here is the code:

\documentclass{article}
\usepackage{fp}% http://ctan.org/pkg/fp
\usepackage{xstring}% http://ctan.org/pkg/xstring
\usepackage{xparse}% http://ctan.org/pkg/xparse
\usepackage{color}

%STRUCT
\newcommand \Rmin[2]{\ensuremath{\FPeval{\result}{round(#1-(#1*#2/100),2)}\result}}
\newcommand \Rmax[2]{\ensuremath{\FPeval{\result}{round(#1+(#1*#2/100),2)}\result}}

\newcommand\defResCMtype[2]{%defined VARIOUS types
    \expandafter\newcommand\csname TOL#1\endcsname{#2}
}
\newcommand\defResCM[3]{%
    \expandafter\newcommand\csname value#1\endcsname{#2}
    \expandafter\newcommand\csname #1min\endcsname{
        \StrDel{#3}{ }[\tmp]% remove spaces and store the string in \tmp
        \IfEqCase{\tmp}{{typeX}{\Rmin{#2}{\TOLtypeX}}
        }%
        [{\color{red}XXXXXX}] %ERROR
    }
    \expandafter\newcommand\csname #1max\endcsname{
        \StrDel{#3}{ }[\tmp]% remove spaces and store the string in \tmp
        \IfEqCase{\tmp}{{typeX}{\Rmax{#2}{\TOLtypeX}}
        }%
        [{\color{red}XXXXXX}] %ERROR
    }
}

%LIB
\defResCMtype{typeX}{5}

\defResCM{compX}{100}{typeX}

%CALC
\newcommand \calc[2]{\ensuremath{\FPeval{\result}{round(#1,#2)}\result}}

\newcommand \testcalcA{\ensuremath{\calc{(105 / 95)}{2}}} %calculated with numbers
\newcommand \testcalcB{\ensuremath{\calc{((\compXmax)/(\compXmin))}{2}}} %calculated with macros -> NOT WORKING


\begin{document}

test = \valuecompX \\
test2= \compXmax \\
test3= \compXmin \\

A = \testcalcA \\ %-> WORKING
%B = \testcalcB \\ %-> NOT WORKING

\end{document}

If I manually enter the numbers created from the test2 & test3 then FPeval calculates the equation A, however, if I want to pass these values automatically as (\compXmax) & (\compXmin) or even comXmax & comXmin in

\newcommand \testcalcB{\ensuremath{\calc{((\compXmax)/(\compXmin))}{2}}}

I get an error ! Use of \@newline doesn't match its definition.\kernel@ifnextchar ...rved@d =#1\def \reserved@a {#2}\def \reserved@b {#3}\f... B = \testcalcB.

Manually inserting numbers between calculations in a document is error prone which I would very much like to avoid, since updating a parameter directly in library would need an update to the whole document where these parameters are used.

Answer 1

The key is you want \compXmin and \compXmax to be evaluated already at their assignment, without the actual calculation embedded in their definitions.

EDITED to allow library to be set in the preamble (which was mentioned in a comment of the OP), through the use of \AtBeginDocument{}. RE-EDITED to save intermediate calculations (\testcalcB result saved in \thetestcalcB, \testcalcC result saved in \thetestcalcC).

\documentclass{article}
\usepackage{fp}% http://ctan.org/pkg/fp
\usepackage{xstring}% http://ctan.org/pkg/xstring
\usepackage{xparse}% http://ctan.org/pkg/xparse
\usepackage{xcolor}

%STRUCT
\newcommand \Rmin[2]{\ensuremath{\FPeval{\result}{round(#1-(#1*#2/100),2)}%
  \xdef\theRmin{\result}}}
\newcommand \Rmax[2]{\ensuremath{\FPeval{\result}{round(#1+(#1*#2/100),2)}%
  \xdef\theRmax{\result}}}

\newcommand\defResCMtype[2]{%defined VARIOUS types
    \expandafter\def\csname TOL#1\endcsname{#2}%
\ignorespaces}
\newcommand\defResCM[3]{%
    \expandafter\def\csname value#1\endcsname{#2}%
        \StrDel{#3}{ }[\tmp]% remove spaces and store the string in \tmp
        \IfEqCase{\tmp}{{typeX}{\Rmin{#2}{\TOLtypeX}\Rmax{#2}{\TOLtypeX}%
                                \expandafter\xdef\csname #1max\endcsname{\theRmax}%
                                \expandafter\xdef\csname #1min\endcsname{\theRmin}%
                               }%
                       }%
        [{\unskip\textcolor{red}{ERROR DEFINING: #1}\par}] %ERROR
\ignorespaces}
%LIB
\AtBeginDocument{
\defResCMtype{typeX}{5}
\defResCM{compX}{100}{typeX}
\defResCMtype{typeX}{10}
\defResCM{altX}{150}{typeX}
\defResCM{compY}{200}{type Y}
}
%CALC
\newcommand \calc[2]{\ensuremath{\FPeval{\result}{round(#1,#2)}}%
                     \xdef\thecalc{\result}}

\newcommand \testcalcB[1]{\ensuremath{\calc{((\csname#1max\endcsname)/%
                          (\csname#1min\endcsname))}{2}}%
                          \edef\thetestcalcB{\thecalc}\thetestcalcB}

\newcommand \testcalcC[1] {\ensuremath{\calc{(\thetestcalcB * \csname#1min\endcsname)}%
                          {2}}\edef\thetestcalcC{\thecalc}\thetestcalcC}
\begin{document}
test = \valuecompX \par
test2= \compXmax \par
test3= \compXmin \par
\medskip
B = \testcalcB{compX} \par %-> NOW WORKING
C = \testcalcC{compX} \par %-> NOW WORKING
\medskip
test = \valuealtX \par
test2= \altXmax \par
test3= \altXmin \par
\medskip
B = \testcalcB{altX} \par %-> NOW WORKING
C = \testcalcC{altX} \par %-> NOW WORKING
\end{document}