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Add a couple of units used by metatrain #217

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a47bd4d
Use electric current instead of charge for dimension analysis
Luthaf May 1, 2026
a93f06f
Add multiple new units
Luthaf May 1, 2026
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12 changes: 11 additions & 1 deletion docs/src/torch/reference/misc.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,10 @@ Supported base units
Unit expressions are built from the following base units. Matching is
case-insensitive, and whitespace is ignored.


**Temperature**:
``Kelvin`` (``K``)

**Length**:
``angstrom`` (``A``), ``Bohr``, ``meter`` (``m``), ``centimeter`` (``cm``),
``millimeter`` (``mm``), ``micrometer`` (``um``, ``µm``), ``nanometer`` (``nm``)
Expand All @@ -35,11 +39,17 @@ case-insensitive, and whitespace is ignored.
``nanosecond`` (``ns``), ``picosecond`` (``ps``), ``femtosecond`` (``fs``)

**Mass**:
``u`` (``Dalton``), ``kilogram`` (``kg``), ``gram`` (``g``), ``electron_mass`` (``m_e``)
``Dalton`` (``u``), ``kilogram`` (``kg``), ``gram`` (``g``), ``electron_mass`` (``m_e``)

**Charge**:
``e``, ``Coulomb`` (``C``)

**Pressure**:
``Pascal`` (``Pa``), ``kiloPascal`` (``kPa``), ``MegaPascal`` (``MPa``), ``GigaPascal`` (``GPa``), ``bar``, ``atm``

**Electric Dipole Moment**:
``Debye`` (``D``)

**Dimensionless**:
``mol``

Expand Down
86 changes: 63 additions & 23 deletions metatomic-torch/src/units.cpp
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Expand Up @@ -26,17 +26,17 @@
*
* @subsection dimensions Dimensional Analysis
*
* Each unit has an associated 5-element dimension vector [L, T, M, Q, Th]
* representing exponents of Length, Time, Mass, Charge, and Temperature.
* For example:
* Each unit has an associated 5-element dimension vector [L, T, M, I, Θ]
* representing exponents of Length, Time, Mass, Electric current, and
* Temperature. For example:
* - Length: [1, 0, 0, 0, 0]
* - Energy: [2, -2, 1, 0, 0] (M L^2 T^-2)
* - Force: [1, -2, 1, 0, 0] (M L T^-2)
* - Pressure: [-1, -2, 1, 0, 0] (M L^-1 T^-2)
*
* Dimensional compatibility is checked by comparing these vectors with a
* tolerance of 1e-10 to accommodate floating-point accumulation from
* fractional powers.
* tolerance of 1e-10 to accommodate floating-point accumulation from fractional
* powers.
*
* @subsection conversion Conversion Factor Calculation
*
Expand All @@ -58,14 +58,16 @@
*/

/// Dimension indices for the 5-element exponent vector.
/// Order: [Length, Time, Mass, Charge, Temperature]
/// Order: [Length, Time, Mass, Electric Current, Temperature]
enum class DimIndex {
LENGTH = 0,
TIME = 1,
MASS = 2,
CHARGE = 3,
TEMPERATURE = 4,
COUNT = 5 // Number of dimensions
LENGTH,
TIME,
MASS,
ELECTRIC_CURRENT,
TEMPERATURE,
// we exclude amount of substance and luminous intensity

COUNT // Number of dimensions
};

/// Physical dimension vector: [Length, Time, Mass, Charge, Temperature]
Expand Down Expand Up @@ -116,11 +118,27 @@ struct Dimension {
return !(*this == other);
}

static const char* dim_index_as_string(size_t index) {
switch (index) {
case static_cast<size_t>(DimIndex::LENGTH):
return "L";
case static_cast<size_t>(DimIndex::TIME):
return "T";
case static_cast<size_t>(DimIndex::MASS):
return "M";
case static_cast<size_t>(DimIndex::ELECTRIC_CURRENT):
return "I";
case static_cast<size_t>(DimIndex::TEMPERATURE):
return "T";
default:
return "<ERROR, should not reach this line>";
}
}

/// Convert dimension to a human-readable string format.
/// Output format: "L^2 M T^-2" style (only non-zero exponents shown).
/// Exponent 1 is omitted, negative exponents use "^-N" format.
std::string to_string() const {
static const char* NAMES[] = {"L", "T", "M", "Q", "Th"};
std::string result;
bool first = true;

Expand All @@ -136,7 +154,7 @@ struct Dimension {
}
first = false;

result += NAMES[i];
result += dim_index_as_string(i);

// Only show exponent if not 1 or -1
if (std::fabs(v - 1.0) >= 1e-10 && std::fabs(v + 1.0) >= 1e-10) {
Expand Down Expand Up @@ -168,15 +186,16 @@ struct UnitValue {
Dimension dim;
};

// Dimension constants for readability
// L T M Q Th
static const Dimension DIM_LENGTH = {{ 1, 0, 0, 0, 0 }};
static const Dimension DIM_TIME = {{ 0, 1, 0, 0, 0 }};
static const Dimension DIM_MASS = {{ 0, 0, 1, 0, 0 }};
static const Dimension DIM_CHARGE = {{ 0, 0, 0, 1, 0 }};
static const Dimension DIM_TEMPERATURE = {{ 0, 0, 0, 0, 1 }};
static const Dimension DIM_ENERGY = {{ 2, -2, 1, 0, 0 }};
static const Dimension DIM_NONE = {{ 0, 0, 0, 0, 0 }};
// Dimension constants for readability L T M I Θ
static const Dimension DIM_LENGTH = {{ 1, 0, 0, 0, 0 }};
static const Dimension DIM_TIME = {{ 0, 1, 0, 0, 0 }};
static const Dimension DIM_MASS = {{ 0, 0, 1, 0, 0 }};
static const Dimension DIM_CHARGE = {{ 0, 1, 0, 1, 0 }};
static const Dimension DIM_TEMPERATURE = {{ 0, 0, 0, 0, 1 }};
static const Dimension DIM_ENERGY = {{ 2, -2, 1, 0, 0 }};
static const Dimension DIM_PRESSURE = {{ -1, -2, 1, 0, 0 }};
static const Dimension DIM_ELECTRIC_DIPOLE = {{ 1, 1, 0, 1, 0 }};
static const Dimension DIM_NONE = {{ 0, 0, 0, 0, 0 }};

/// Lowercase a string in place and return it.
static std::string to_lower(std::string s) {
Expand All @@ -194,6 +213,10 @@ static std::string to_lower(std::string s) {
/// Case-insensitive lookup: names are lowercased before searching.

static const auto BASE_UNITS = std::unordered_map<std::string, UnitValue>{
// --- Temperature ---
{"kelvin", {1.0, DIM_TEMPERATURE}},
{"k", {1.0, DIM_TEMPERATURE}},

// --- Length ---
{"angstrom", {1e-10, DIM_LENGTH}},
{"a", {1e-10, DIM_LENGTH}},
Expand All @@ -211,6 +234,7 @@ static const auto BASE_UNITS = std::unordered_map<std::string, UnitValue>{
{"micrometer", {1e-6, DIM_LENGTH}},

// --- Energy ---
{"electronvolt", {1.602176634e-19, DIM_ENERGY}},
{"ev", {1.602176634e-19, DIM_ENERGY}},
{"mev", {1.602176634e-19 * 1e-3, DIM_ENERGY}},
{"hartree", {4.359744722206048e-18, DIM_ENERGY}},
Expand Down Expand Up @@ -251,6 +275,22 @@ static const auto BASE_UNITS = std::unordered_map<std::string, UnitValue>{
{"coulomb", {1.0, DIM_CHARGE}},
{"c", {1.0, DIM_CHARGE}},

// --- Pressure ---
{"pa", {1.0, DIM_PRESSURE}},
{"pascal", {1.0, DIM_PRESSURE}},
{"kpa", {1e3, DIM_PRESSURE}},
{"kilopascal", {1e3, DIM_PRESSURE}},
{"mpa", {1e6, DIM_PRESSURE}},
{"megapascal", {1e6, DIM_PRESSURE}},
{"gpa", {1e9, DIM_PRESSURE}},
{"gigapascal", {1e9, DIM_PRESSURE}},
{"bar", {100000.0, DIM_PRESSURE}},
{"atm", {101325.0, DIM_PRESSURE}},

// --- Electric dipole moment ---
{"debye", {1/299792458.0 * 1e-21, DIM_ELECTRIC_DIPOLE}},
{"d", {1/299792458.0 * 1e-21, DIM_ELECTRIC_DIPOLE}},

// --- Dimensionless ---
{"mol", {6.02214076e23, DIM_NONE}},

Expand Down
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