Declarations

Every name that appears in the model must first be declared as a variable or a parameter.

Endogenous variables: var

The var keyword declares one or more endogenous variables, optionally qualified by their dynamic role:

var(state) K, A;          // predetermined: pinned at t=0 by initval
var(jump)  C;             // forward-looking: pinned at t=T by terminal SS
var        Y, r;          // unqualified = algebraic (no time derivative)

The three roles are:

state (predetermined)

Carries a time derivative — i.e. diff(state) appears in exactly one equation of the model block — and is pinned at t=0 by an initval block.

jump (forward-looking)

Also carries a time derivative, but is not pinned at t=0; the solver anchors it at the terminal steady state. This is the continuous-time analogue of a Dynare jumper/forward variable.

var (no qualifier)

Algebraic: no time derivative, defined by a static equation.

The role is declared, not inferred: the IR validates each declared role against how the variable is used in the equations and rejects inconsistencies (e.g. a var(state) whose diff(.) never appears, or a variable both differentiated and pinned by a static equation).

The qualifier may also carry a domain constraint (positive / negative / boundaries=(lo, hi)) that keeps the variable strictly inside a known range when the steady state is solved numerically — see Domain constraints.

Exogenous processes: varexo

varexo declares one or more exogenous (forcing) variables — the names that appear on the right of var X; path = …; in the shocks block:

varexo e, delta;

Inside the model block, a varexo is read like any other name; the solver provides its time-varying value at each grid point from the active shock path. See The shocks block for the path syntax.

Parameters: parameters and assignments

parameters declares the names; values are assigned afterwards by ordinary name = expression; statements:

parameters alpha, delta, rho;
alpha = 0.33;
delta = 0.10;
rho   = 0.05;

Parameter values may reference previously-assigned parameters and any literal expression that the model language accepts (arithmetic, exp, log, sqrt, …). They are resolved once at solve time.

Special names

A few identifiers carry a built-in meaning and should not be reused as variable names. (The grammar does not reserve them — they tokenise as ordinary identifiers — but each is special-cased downstream, so using one as a declared name is unsupported.) t is the (continuous) time variable: inside the shocks block, and inside model and steady_state_model blocks the time argument at which the expression is evaluated. diff and if are built-in functions; steady_state is the steady-state callable. The shock-shape helpers (step, pulse, ramp, bump, expdecay, smoothstep) are built-in inside shocks blocks only.