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56 lines
2.7 KiB
56 lines
2.7 KiB
2 years ago
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\chapter{Predefined Variables}\label{ch:predefined}
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A few commonly used variables are predefined in
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\aprepro{}\footnote{The units system described in
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Chapter~\ref{ch:units} also predefines several variables when it is
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activated}. These are listed below. The default output format
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\cmd{\_FORMAT} is specified as a C language format string, see your C
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language documentation for more information. The default output format
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(\cmd{\_FORMAT}) and comment (\cmd{\_C\_}) variables are defined with
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a leading underscore in their name so they can be redefined without
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generating an error message.
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\begin{longtable}{lll}
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\caption{Predefined Variables}\\
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Name & Value & Description \\
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\hline
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PI & 3.14159265358979323846 & $\pi$ \\
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PI\_2 & 1.57079632679489661923 & $\pi/2$ \\
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TAU & 6.28318530717958623200 & $2\pi$ \\
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SQRT2 & 1.41421356237309504880 & $\sqrt{2}$ \\
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DEG & 57.2957795130823208768 & $180/\pi$ degrees per radian \\
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RAD & 0.01745329251994329576 & $\pi/180$ radians per degree \\
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E & 2.71828182845904523536 & base of natural logarithm \\
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GAMMA & 0.57721566490153286060 & $\gamma$, euler-mascheroni constant \\
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PHI & 1.61803398874989484820 & golden ratio $(\sqrt{5}+1)/2$ \\
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VERSION & Varies, string value & current version of \aprepro \\
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\_FORMAT& \texttt{"}\%.10g\texttt{"} & default output format \\
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\_C\_ & \texttt{"}\$\texttt{"} & default comment character \\
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\end{longtable}
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Note that the output format is used to output both integers and floating point
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numbers. Therefore, it should use the \%g format descriptor which will use either
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the decimal (\%d), exponential (\%e), or float (\%f) format, whichever is shorter,
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with insignificant zeros suppressed. The table below illustrates the effect of
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different format specifications on the output of the variable \textbf{PI} and the
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value 1.0 . See the documentation of your C compiler for more information. For
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most cases, the default value is sufficient.
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\begin{longtable}{lll}
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\caption{Effect of various output format specifications}\\
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Format & PI Output & 1.0 Output \\
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\hline
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\%.10g & 3.141592654 & 1 \\
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\%.10e & 3.1415926536e+00 & 1.0000000000e+00 \\
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\%.10f & 3.1415926536 & 1.0000000000 \\
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\%.10d & 1413754136 & 0000000000 \\
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\end{longtable}
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The comment character should be set to the character that the program
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which will read the processed file uses as a comment character. The
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default value of \texttt{"}\$\texttt{"} is the comment character used
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by the SEACAS codes at Sandia National Laboratories. The \textbf{-c}
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command line option (described in Chapter~\ref{ch:execution}) changes
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the value of the comment variable to match the character specified on
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the command line.
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