llnl / units

Units What's new Documentation The Units library provides a means of working with units of measurement at runtime, including conversion to and from strings. It provides a small number of types for working with units and measurements and operations necessary for user input and output with units. This software was developed for use in LLNL/GridDyn, and HELICS and is currently a work in progress (though it's getting close). Namespaces, function names, and code organization are subject to change, though they are fairly stable at this point. Feedback is welcome. A set of documentation is available. A Python wrapper is also available through Pypi that wraps a limited subset of the library for most common purposes. Table of contents • Purpose • Limitations • Alternatives • C++ Types • Unit Representation • Building The Library • Try it out • Usage • Units • Measurements • String Conversions • Contributions • Users • Release Purpose A units library was needed to represent units from a wide range of disciplines and be able to separate them from the numerical values for use in calculations when needed. The main drivers are • converting units, often represented by strings, to a standardized unit set when dealing with user input and output. • Being able to use the unit as a single type that could contain any unit, and not introduce a huge number of types to represent all possible units. • Being able to associate a completely arbitrary unit given by users with a generic interface and support conversions between those user defined units and other units. • The library has its origins in power systems so support for per-unit operations was also lacking in the alternatives. • Capturing uncertainty and uncertainty calculations directly with a measurement It was desired that the unit representation be a compact type ( or < conditions then check for equality if needed. There are a few situations that are not totally consistent like and , but such is nature of floating point operations. So, from a mathematical purity sense this isn't consistent but does mostly what was needed. If the difference between the two values is a subnormal number the equality comparison also evaluates to true, even if that would otherwise be outside the numerical tolerance. Defined units There are 2 sets of defined units, many common units are defined in the namespace, many others are defined in and subnamespaces. See Defined Units for details on the available units. Physics constants A set of physical and numerical constants are defined in the namespace. More details a _...truncated for preview_