Declarations

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model Name { ... } contains declarations and simultaneous relations. Semicolons end declarations; // introduces a comment and /// attaches documentation. Names are case-sensitive.

declarations.eqi

model Current(parameter voltage: kg * m ^ 2 / (s ^ 3 * A) = 12, parameter resistance: kg * m ^ 2 / (s ^ 3 * A ^ 2) = 4) {
  variable current: A;
  relation ohm {
    voltage - resistance * current = 0;
  }
}

Declaration	Meaning in this example
parameter voltage: dimension = 12;	A fixed mathematical input of 12 coherent SI units; voltage here is measured in volts.
variable current: A;	An unknown current, not a Python variable or a command to compute it immediately.
relation ohm { ... }	An equation constraining those values; declaration order is not execution order.

An algebraic variable needs no declaration initial value. An evolving scalar uses state x: 1; initial { x = 1; } to declare its role and initial equation; see Equations and state. 1 denotes a dimensionless type. Do not interpret an omitted initial value as a promise of zero initialization.

Spatial declarations

A spatial unknown also names its exact support. In the complete elastic-body example, variable displacement: vector<m, 2> on body; means a vector displacement on body, in metres. The enclosing domain body = box(...) supplies the two-dimensional support. The compiler supplies the admitted continuum Representation; source declarations do not select a mesh or finite-element space.

Scalar and vector declarations are not interchangeable. Component support and Field requirements bind existing occurrences; see Composition.

Example source · declaration parser · Next: Quantities and units