# constants: Update to 2018 CODATA values

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The **constants** package contains CODATA internationally recommended values of the fundamental physical constants, provided as symbols for direct use within the R language. Optionally, the values with uncertainties and/or units are also provided if the **errors**, **units** and/or **quantities** packages are installed. The Committee on Data for Science and Technology (CODATA) is an interdisciplinary committee of the International Council for Science which periodically provides the internationally accepted set of values of the fundamental physical constants. This release contains the “2018 CODATA” version, published on May 2019 [E. Tiesinga, P. J. Mohr, D. B. Newell, and B. N. Taylor (2020) http://physics.nist.gov/constants].

This version contains some breaking changes that are necessary to streamline future updates and provide a stable symbol table:

- The
`codata`

table includes the absolute uncertainty instead of the relative one. Thus, the`rel_uncertainty`

column has been dropped in favour of the new`uncertainty`

. Also, columns have been slightly reordered. - Symbol names for constants have changed. The old ones were hand-crafted and thus unmanageable. This release adopts the ASCII symbols defined by NIST in their webpage, except for those that collide with some base R function. In particular, there are two cases:
`c`

, the speed of light, has been renamed as`c0`

;`sigma`

, the Stefan-Boltzmann constant, has been renamed as`sigma0`

. - Constant types, or categories, (column
`codata$type`

) adopts the names defined by NIST in the webpage too. Some constants belong to more than one category (separated by comma); some others belong to no category (missing type).

There are some new features too:

- In addition to the
`codata`

data frame, this release includes`codata.cor`

, a correlation matrix for all the constants. - In addition to
`syms_with_errors`

and`syms_with_units`

, there is a new list of symbols called`syms_with_quantities`

(available if the optional`quantities`

package is installed), which provides constant values with uncertainty**and**units. - Experimental support for correlated values in
`syms_with_errors`

and`syms_with_quantities`

is provided (disabled by default; see details in`help(syms)`

for activation instructions).

See the README for some usage examples. For questions, suggestions or issues, please use the issue tracker.

*Article originally published in Enchufa2.es: constants: Update to 2018 CODATA values*.

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