While I don't think this is necessary in many cases, now that you ask, I want this too. So, I built something.
from scipy.constants import physical_constants as pc
import re
from math import ceil
filename = r'physical_constants.tex'
setup = r"""
\RequirePackage{etoolbox}
\RequirePackage{xparse}
\RequirePackage{siunitx}
\makeatletter
\def\physicalconstants@missingconstantmarker#1{%
\ifx@onlypreamble@notprerr% only insert the marker when not in preamble
{\textbf{??#1??}}%
\fi
}
\def\physicalconstants@declare#1#2#3#4#5{% {name}{value}{unit}{uncertainty}
\csdef{physicalconstants@#1@value}{#2}%
\csdef{physicalconstants@#1@unit}{#3}%
\csdef{physicalconstants@#1@uncertainty}{#4}%
\csdef{physicalconstants@#1@uncertainvalue}{#5}%
}
\def\physicalconstants@blind@get#1#2{% {entry}{name}
\csuse{physicalconstants@#2@#1}%
}
\def\physicalconstants@try#1{% {name}{subject}, gobbles subject if name is undefined
\ifcsdef{physicalconstants@#1@value}{%
@firstofone
}{%
\GenericWarning{}{LaTeX Warning: I do not know the physical constant `#1'.}%
\physicalconstants@missingconstantmarker{#1}%
@gobble
}%
}
\def\physicalconstants@declarealias#1#2{% {new}{old}
\physicalconstants@try{#2}{%
\csdef{physicalconstants@#1@value}{\physicalconstants@blind@get{value}{#2}}%
\csdef{physicalconstants@#1@unit}{\physicalconstants@blind@get{unit}{#2}}%
\csdef{physicalconstants@#1@uncertainty}{\physicalconstants@blind@get{uncertainty}{#2}}%
\csdef{physicalconstants@#1@uncertainvalue}{\physicalconstants@blind@get{uncertainvalue}{#2}}%
}%
}
\def\physicalconstants@get#1#2{% {entry}{name}
\physicalconstants@try{#2}{%
\physicalconstants@blind@get{#1}{#2}%
}%
}
\NewDocumentCommand\pcalias{}{% {new}{old}}
\physicalconstants@declarealias
}
\NewDocumentCommand\pcget{}{% {entry}{name}
\physicalconstants@get
}
\NewDocumentCommand\pcvalue{O{} m}{% [\num options]{name}
\physicalconstants@try{#2}{%
\num[#1]{\physicalconstants@blind@get{value}{#2}}%
}%
}
\NewDocumentCommand\pcunit{O{} m}{% [\si options]{name}
\physicalconstants@try{#2}{%
\si[#1]{\physicalconstants@blind@get{unit}{#2}}%
}%
}
\NewDocumentCommand\pcuncertainty{O{} m}{% [\num options]{name}
\physicalconstants@try{#2}{%
\num[#1]{\physicalconstants@blind@get{uncertainty}{#2}}%
}%
}
\NewDocumentCommand\pcuncertainvalue{O{} m}{% [\num options]{name}
\physicalconstants@try{#2}{%
\num[#1]{\physicalconstants@blind@get{uncertainvalue}{#2}}%
}%
}
\NewDocumentCommand\pc{O{} m}{% [\SI options]{name}
\physicalconstants@try{#2}{%
\SI[#1]{\physicalconstants@blind@get{value}{#2}}{\physicalconstants@blind@get{unit}{#2}}%
}%
}
\NewDocumentCommand\pcu{O{} m}{% [\num options]{name}
\physicalconstants@try{#2}{%
\SI[#1]{\physicalconstants@blind@get{uncertainvalue}{#2}}{\physicalconstants@blind@get{unit}{#2}}%
}%
}
"""
cleanup = r"""
\makeatother
"""
unit_map = {
'A': r'\ampere',
'C': r'\coulomb',
'F': r'\farad',
'GeV': r'\giga\electronvolt',
'Hz': r'\hertz',
'J': r'\joule',
'K': r'\kelvin',
'MHz': r'\mega\hertz',
'MeV': r'\mega\electronvolt',
'N': r'\newton',
'Pa': r'\pascal',
'S': r'\siemens',
'T': r'\tesla',
'V': r'\volt',
'W': r'\watt',
'Wb': r'\weber',
'c': r'\clight',
'eV': r'\electronvolt',
'fm': r'\femto\meter',
'kg': r'\kilogram',
'm': r'\metre',
'mol': r'\mole',
'ohm': r'\ohm',
's': r'\second',
'sr': r'\steradian',
'u': r'\atomicmassunit',
}
unit_regex = re.compile(r'\b([a-zA-Z]+)(?:^(-?)(\d+))?\b')
number_regex = re.compile(r'([+-]?)(\d+)(.?)(\d)(e?)([+-]?\d)')
def format_unit(unit_input):
unit = ''
for (base, sign, exp) in unit_regex.findall(unit_input):
if sign:
unit += r'\per'
if exp == '1':
pass
elif exp == '2':
unit += r'\square'
elif exp == '3':
unit += r'\cube'
elif exp:
unit += r'\raiseto{{{}}}'.format(exp)
unit += unit_map[base]
return unit
def format_uncertain_value(value_input, uncertainty_input):
val_parts = number_regex.fullmatch(str(value_input)).groups()
unc_parts = number_regex.fullmatch(str(uncertainty_input)).groups()
unc_digits = unc_parts[1] + unc_parts[3]
if int(unc_digits):
val_exp = int(val_parts[5]) if val_parts[5] else 0
unc_exp = int(unc_parts[5]) if unc_parts[5] else 0
exp_discrepancy = ( (unc_exp - len(unc_parts[3]))
- (val_exp - len(val_parts[3])) )
if exp_discrepancy < 0:
# The uncertainty is too granular, we have to round.
unc_digits = str(ceil(float('{}e{}'.format(unc_digits, exp_discrepancy))))
else:
# The uncertainty is missing some zeros at the end.
unc_digits += '0' * exp_discrepancy
else:
unc_digits = '0'
return '{0}{1}{2}{3}({6}){4}{5}'.format(*val_parts, unc_digits)
def main():
with open(filename, 'w') as of:
of.write(setup)
for (name, entries) in pc.items():
(value, unit, uncertainty) = entries
of.write(r'\physicalconstants@declare{{{}}}{{{}}}{{{}}}{{{}}}{{{}}}'.format(
name,
value,
format_unit(unit),
uncertainty,
format_uncertain_value(value, uncertainty))
+ '\n')
of.write(cleanup)
if name == 'main':
main()
This Python script will create the file physical_constants.tex with all the constants in scipy.constants.physical_constants. You can \input it into your preamble and use it with all the usual siunitx goodies.
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[
locale=DE,
per-mode=fraction,
quotient-mode=fraction,
]{siunitx}
\let\vectimes\times
\let\times\cdot
\input{physical_constants}
\pcalias{e}{elementary charge}
\pcalias{aSi}{lattice parameter of silicon}
\begin{document}
\pcvalue{aSi}
\pcunit{aSi}
\pcuncertainty{aSi}
\pcuncertainvalue{aSi}
\pc{aSi}
\pcu{aSi}
\pcu[separate-uncertainty]{aSi}
\pc{e}
\end{document}
I have not tested this extensively, nor have I put an awful lot of thought into the design. Use at your own discretion. Feedback and suggestions are, of course, welcome. If I am wrong and this sparks a lot of interest, it may be worth the effort to make it a full fledged package.
