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如何从数值结果中获取工程倍数符号

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如何从数值结果中获取工程倍数符号

numerica 包是解决电路方程的非常方便的工具，但我找不到使用 mA、kV 等工程倍数来获取数值结果的方法。siunitx 包有一个非常好的解决方案，如下所示，但我无法在管道中获取这两个包，因为宏扩展最初不是一个简单的文本结果。

\documentclass{article}

\usepackage{amssymb} %maths
\usepackage{amsmath} %maths
\usepackage{physics} % before numerica!!!
\usepackage{numerica} % computation of math expressions
\def\eval{\nmcEvaluate} % to simplify numerica avoiding conflict with physics
\usepackage{siunitx}
% --- siunitx settings -----
\sisetup {
    exponent-to-prefix  = true,       % convert exponents into belonging prefixes
    round-mode          = places,
    round-precision     = 2,
    scientific-notation = engineering,% try to use next engineering unit instead of '.'
    per-mode            = symbol,
    per-symbol          = /
}% --------------------------

\begin{document}

Numerica is used to solve the Ohm's Law $I_B = VCC/R1$, given $R1= \SI{10}{\kilo\ohm}$ and $VCC= \SI{5}{\volt}$  as follows: \eval[vv=, eq=\approx]{$I_B$}[I_B = VCC/R1, R1=10^4,  VCC=5.0][2x] A.

However, the result uses scientific notation instead of engineering multiples notation that is nicely provided by siunitx as follows: $ V_B \approx \num{5e-4}$A, or even better in a compact form \SI{5e-4}{\ampere}.

I tried a naive approach to mix the two packages siunitx and numerica but it doesn't work.
% \SI{\eval[vv=, eq=\approx]{$I_B$}[I_B = VCC/R1, R1=10^4,  VCC=5.0][2x]}{\ampere}

\end{document} '''

答案1

目前，我能想到的唯一实现所需结果的方法是使用numerica命令\reuse，该命令将计算结果保存到宏中（然后可以在当前文档的其他地方使用，也可以保存到文件中；请参阅手册第 6.4 节numerica）。我选择ohmslaw以下宏的名称：

\documentclass{article}

\usepackage{amssymb} %maths
\usepackage{amsmath} %maths
\usepackage{physics} % before numerica!!!
\usepackage{numerica} % computation of math expressions
\def\eval{\nmcEvaluate} % to simplify numerica avoiding conflict with physics
\usepackage{siunitx}
% --- siunitx settings -----
\sisetup {
    exponent-to-prefix  = true,       % convert exponents into belonging prefixes
    round-mode          = places,
    round-precision     = 2,
    scientific-notation = engineering,% try to use next engineering unit instead of '.'
    per-mode            = symbol,
    per-symbol          = /
}% --------------------------

\begin{document}

\eval[vv=, eq=\approx]{$I_B$}[I_B = VCC/R1, R1=10^4,  VCC=5.0][5] A.
\reuse[renew]{ohmslaw}

\SI{\ohmslaw}{\ampere}.

\end{document} '''

Note that I saved the calculated result in ordinary decimal notation rather than scientific notation (the 5 rather than your 2x in the trailing number format option of ```\eval```).

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