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'''DATA''' instances are used to pass 'additional parameters' to [[External_relation|external relations]]. This can be used for example to define constants that are required for calculation of the external relation, but which do not vary over the duration of a simulation.

DATA instances are used for example in [[FPROPS]] to specify the fluid being used:

<source lang="a4c">MODEL ammoniadata;
component IS_A symbol_constant;
component :== 'ammonia';

END ammoniadata;

MODEL example;

(* variables that will be calculated (or specified, in some cases *)
p IS_A pressure;

T IS_A temperature;
rho IS_A mass_density;
h IS_A specific_enthalpy;

(* this is the 'DATA' instance that will be passed to the external relation *)
propsdata IS_A ammoniadata;

(* declare the external relation, together with the variables and DATA that it uses *)
props1: helmholtz_p(

T, rho : INPUT;
p : OUTPUT;

propsdata : DATA
);
END example;</source>

See also [[External_libraries#DATA_instance]].

[[Category:Syntax]]
[[Category:Documentation]]

DATA - Revision history

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