Add 'Units' class for doing conversions with dimensionality checks
Introduces a new, more natural notation for writing unit strings, for use in YAML input files. Unlike 'toSI', conversions are checked for dimensional consistency.
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Ray Speth
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4 changed files with 318 additions and 1 deletions
95
include/cantera/base/Units.h
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95
include/cantera/base/Units.h
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/**
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* @file Units.h
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* Header for unit conversion utilities, which are used to translate
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* user input from input files (See \ref inputfiles and
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* class \link Cantera::Units Units\endlink).
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*/
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// This file is part of Cantera. See License.txt in the top-level directory or
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// at https://www.cantera.org/license.txt for license and copyright information.
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#ifndef CT_UNITS_H
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#define CT_UNITS_H
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#include "cantera/base/ct_defs.h"
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namespace Cantera
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{
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//! A representation of the units associated with a dimensional quantity.
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/*!
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* Used for converting quantities between unit systems and checking for
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* dimensional consistency. Units objects are mainly used within UnitSystem
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* class to convert values from a user-specified Unit system to Cantera's
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* base units (SI + kmol).
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*/
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class Units
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{
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public:
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//! Create a Units object with the specified dimensions.
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explicit Units(double factor=1.0, double mass=0, double length=0,
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double time=0, double temperature=0, double current=0,
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double quantity=0);
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//! Create an object with the specified dimensions
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explicit Units(const std::string& name);
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//! Returns `true` if the specified Units are dimensionally consistent
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bool convertible(const Units& other) const;
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//! Return the factor for converting from this unit to Cantera's base
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//! units.
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double factor() const { return m_factor; }
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//! Multiply two Units objects, combining their conversion factors and
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//! dimensions
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Units& operator*=(const Units& other);
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//! Provide a string representation of these Units
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std::string str() const;
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private:
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//! Scale the unit by the factor `k`
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void scale(double k) { m_factor *= k; }
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//! Raise these Units to a power, changing both the conversion factor and
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//! the dimensions of these Units.
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Units pow(double expoonent) const;
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double m_factor; //!< conversion factor to Cantera base units
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double m_mass_dim;
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double m_length_dim;
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double m_time_dim;
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double m_temperature_dim;
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double m_current_dim;
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double m_quantity_dim;
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friend class UnitSystem;
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};
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//! Unit conversion utility
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/*!
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* String representations of units can be written using multiplication,
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* division, and exponentiation. Spaces are ignored. Positive, negative, and
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* decimal exponents are permitted. Examples:
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*
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* kg*m/s^2
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* J/kmol
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* m*s^-2
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* J/kg/K
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*
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* @ingroup inputfiles
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*/
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class UnitSystem
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{
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public:
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//! Convert `value` from the units of `src` to the units of `dest`.
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double convert(double value, const std::string& src,
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const std::string& dest) const;
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double convert(double value, const Units& src, const Units& dest) const;
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};
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}
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#endif
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190
src/base/Units.cpp
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190
src/base/Units.cpp
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//! @file Units.cpp
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// This file is part of Cantera. See License.txt in the top-level directory or
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// at https://www.cantera.org/license.txt for license and copyright information.
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#include "cantera/base/Units.h"
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#include "cantera/base/ctexceptions.h"
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#include "cantera/base/global.h"
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#include "cantera/base/stringUtils.h"
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#include "cantera/base/AnyMap.h"
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namespace {
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using namespace Cantera;
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const std::map<std::string, Units> knownUnits{
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{"", Units(1.0)},
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{"1", Units(1.0)},
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// Mass [M]
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{"kg", Units(1.0, 1, 0, 0)},
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{"g", Units(1e-3, 1, 0, 0)},
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// Length [L]
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{"m", Units(1.0, 0, 1, 0)},
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{"micron", Units(1e-6, 0, 1, 0)},
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{"angstrom", Units(1e-10, 0, 1, 0)},
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{"Å", Units(1e-10, 0, 1, 0)},
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// Time [T]
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{"s", Units(1.0, 0, 0, 1)},
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{"min", Units(60, 0, 0, 1)},
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{"hr", Units(3600, 0, 0, 1)},
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// Temperature [K]
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{"K", Units(1.0, 0, 0, 0, 1)},
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{"C", Units(1.0, 0, 0, 0, 1)},
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// Current [A]
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{"A", Units(1.0, 0, 0, 0, 0, 1)},
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// Quantity [Q]
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{"mol", Units(1e-3, 0, 0, 0, 0, 0, 1)},
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{"gmol", Units(1e-3, 0, 0, 0, 0, 0, 1)},
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{"mole", Units(1e-3, 0, 0, 0, 0, 0, 1)},
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{"kmol", Units(1.0, 0, 0, 0, 0, 0, 1)},
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{"kgmol", Units(1.0, 0, 0, 0, 0, 0, 1)},
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{"molec", Units(1.0/Avogadro, 0, 0, 0, 0, 0, 1)},
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// Energy [M*L^2/T^2]
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{"J", Units(1.0, 1, 2, -2)},
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{"cal", Units(4.184, 1, 2, -2)},
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{"erg", Units(1e-7, 1, 2, -2)},
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{"eV", Units(ElectronCharge, 1, 2, -2)},
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// Pressure [M/L/T^2]
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{"Pa", Units(1.0, 1, -1, -2)},
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{"atm", Units(OneAtm, 1, -1, -2)},
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{"bar", Units(1.0e5, 1, -1, -2)},
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// Volume [L^3]
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{"m^3", Units(1.0, 0, 3, 0)},
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{"liter", Units(0.001, 0, 3, 0)},
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{"L", Units(0.001, 0, 3, 0)},
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{"l", Units(0.001, 0, 3, 0)},
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{"cc", Units(1.0e-6, 0, 3, 0)},
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// Other electrical units
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{"ohm", Units(1.0, 1, 2, -3, 0, -2)}, // kg*m^2/s^3/A^2
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{"V", Units(1.0, 1, 2, -3, 0, -1)}, // kg*m^2/s^3/A
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{"coulomb", Units(1.0, 0, 0, 1, 0, 1)}, // A*s
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};
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}
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namespace Cantera
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{
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Units::Units(double factor, double mass, double length, double time,
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double temperature, double current, double quantity)
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: m_factor(factor)
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, m_mass_dim(mass)
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, m_length_dim(length)
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, m_time_dim(time)
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, m_temperature_dim(temperature)
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, m_current_dim(current)
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, m_quantity_dim(quantity)
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{
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}
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Units::Units(const std::string& name)
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: m_factor(1.0)
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, m_mass_dim(0)
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, m_length_dim(0)
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, m_time_dim(0)
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, m_temperature_dim(0)
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, m_current_dim(0)
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, m_quantity_dim(0)
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{
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size_t start = 0;
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while (true) {
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// Split into groups of the form 'unit^exponent'
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size_t stop = name.find_first_of("*/", start);
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size_t carat = name.find('^', start);
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if (carat > stop) {
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// No carat in this group
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carat = npos;
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}
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std::string unit = trimCopy(
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name.substr(start, std::min(carat, stop) - start));
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double exponent = 1.0;
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if (carat != npos) {
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exponent = fpValueCheck(name.substr(carat+1, stop-carat-1));
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}
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if (start != 0 && name[start-1] == '/') {
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// This unit is in the denominator
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exponent = -exponent;
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}
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if (knownUnits.find(unit) != knownUnits.end()) {
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// Incorporate the unit defined by the current group
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*this *= knownUnits.at(unit).pow(exponent);
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} else {
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throw CanteraError("Units::Units(string)",
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"Unknown unit '{}' in unit string '{}'", unit, name);
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}
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start = stop+1;
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if (stop == npos) {
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break;
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}
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}
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}
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bool Units::convertible(const Units& other) const
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{
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return (m_mass_dim == other.m_mass_dim &&
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m_length_dim == other.m_length_dim &&
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m_time_dim == other.m_time_dim &&
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m_temperature_dim == other.m_temperature_dim &&
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m_current_dim == other.m_current_dim &&
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m_quantity_dim == other.m_quantity_dim);
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}
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Units& Units::operator*=(const Units& other)
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{
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m_factor *= other.m_factor;
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m_mass_dim += other.m_mass_dim;
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m_length_dim += other.m_length_dim;
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m_time_dim += other.m_time_dim;
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m_temperature_dim += other.m_temperature_dim;
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m_current_dim += other.m_current_dim;
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m_quantity_dim += other.m_quantity_dim;
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return *this;
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}
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Units Units::pow(double exponent) const {
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return Units(std::pow(m_factor, exponent),
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m_mass_dim * exponent,
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m_length_dim * exponent,
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m_time_dim * exponent,
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m_temperature_dim * exponent,
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m_current_dim * exponent,
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m_quantity_dim * exponent);
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}
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std::string Units::str() const {
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return fmt::format("Units({} kg^{} * m^{} * s^{} * K^{} * A^{} * kmol^{})",
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m_factor, m_mass_dim, m_length_dim, m_time_dim,
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m_temperature_dim, m_current_dim, m_quantity_dim);
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}
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double UnitSystem::convert(double value, const std::string& src,
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const std::string& dest) const
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{
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return convert(value, Units(src), Units(dest));
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}
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double UnitSystem::convert(double value, const Units& src,
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const Units& dest) const
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{
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if (!src.convertible(dest)) {
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throw CanteraError("UnitSystem::convert",
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"Incompatible units:\n {} and\n {}", src.str(), dest.str());
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}
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return value * src.factor() / dest.factor();
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}
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}
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@ -8,7 +8,7 @@
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*/
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// This file is part of Cantera. See License.txt in the top-level directory or
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// at http://www.cantera.org/license.txt for license and copyright information.
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// at https://www.cantera.org/license.txt for license and copyright information.
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#ifndef CT_UNITS_H
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#define CT_UNITS_H
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32
test/general/test_units.cpp
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32
test/general/test_units.cpp
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#include "gtest/gtest.h"
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#include "cantera/base/Units.h"
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using namespace Cantera;
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TEST(Units, convert_to_base_units) {
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UnitSystem U;
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EXPECT_DOUBLE_EQ(U.convert(1.0, "Pa", "kg/m/s^2"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "J", "kg*m^2/s^2"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "ohm", "kg*m^2/s^3/A^2"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "V", "kg*m^2/A*s^-3"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "coulomb", "A*s"), 1.0);
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}
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TEST(Units, notation) {
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UnitSystem U;
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EXPECT_DOUBLE_EQ(U.convert(2.0, "m^2", "m*m"), 2.0);
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EXPECT_DOUBLE_EQ(U.convert(3.0, "", "kg/kg"), 3.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "1/m^2", "m^-2"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(4.0, "s^3", "s^5/s^2"), 4.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, "kg * m/s ^2", "s^-2*kg*m"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(1.0, " kg*m / s^ 2", "s ^-2 * kg*m"), 1.0);
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}
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TEST(Units, basic_conversions) {
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UnitSystem U;
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EXPECT_DOUBLE_EQ(U.convert(100, "cm", "m"), 1.0);
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EXPECT_DOUBLE_EQ(U.convert(2, "kmol", "mol"), 2000);
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EXPECT_DOUBLE_EQ(U.convert(1000, "cal", "J"), 4184);
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EXPECT_DOUBLE_EQ(U.convert(2, "m^3", "l"), 2000);
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EXPECT_DOUBLE_EQ(U.convert(1, "atm", "Pa"), 101325);
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}
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