SELECT - Revision history

Jpye at 08:05, 15 August 2010

2010-08-15T08:05:37Z

← Older revision		Revision as of 08:05, 15 August 2010
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	The '''SELECT''' statement is used to selectively compile equations according to the value of constants in the model. This similar to the [[WHEN]] statement used in [[Conditional modelling]], except that it allows no possibility of equations being switched on or off after the model is instantiated.		The '''SELECT''' statement is used to selectively compile equations according to the value of constants in the model. This similar to the [[WHEN]] statement used in [[Conditional modelling]], except that it allows no possibility of equations being switched on or off after the model is instantiated.


	Be careful when naming your equations inside a SELECT statement: A name cannot be defined two different ways inside the SELECT statement, but it may be defined outside the case statement and then ''refined'' in different ways in separate cases, using [[IS_REFINED_TO]].		Be careful when naming your equations inside a SELECT statement: A name cannot be defined two different ways inside the SELECT statement, but it may be defined outside the case statement and then ''refined'' in different ways in separate cases, using [[IS_REFINED_TO]].
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	In fact, this is the technique used in the current {{src\|models/components.a4l}} model in our [[ModelLibrary]].		In fact, this is the technique used in the current {{src\|models/components.a4l}} model in our [[ModelLibrary]].

			See also [[Conditional modelling]], [[IF]], [[WHEN]], and [[SWITCH]].

	~~See also [[Conditional modelling]].~~		[[Category:Syntax]]




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

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The '''SELECT''' statement is used to selectively compile equations according to the value of constants in the model. This similar to the [[WHEN]] statement used in [[Conditional modelling]], except that it allows no possibility of equations being switched on or off after the model is instantiated.

Be careful when naming your equations inside a SELECT statement: A name cannot be defined two different ways inside the SELECT statement, but it may be defined outside the case statement and then ''refined'' in different ways in separate cases, using [[IS_REFINED_TO]].

This statement is declarative. Order of the CASEs does not matter. All matching cases are executed. The OTHERWISE is executed if present and no other CASEs match. SELECT is not
allowed inside [[FOR]], but writing [[FOR]] statements inside SELECT is allowed.

<source lang="a4c">MODEL eos_constants (

component_name WILL_BE symbol_constant;
);
T_c IS_A temperature_constant;
p_c IS_A pressure_constant;

(* depending on the value of the 'component_name' parameter, set the
critical temperature and pressure to the appropriate value. *)
SELECT(component_name)
CASE 'hydrogen':

T_c :== 33 {K};
p_c :== 12.9 {bar};

CASE 'water':
T_c :== 647.3 {K};
p_c :== 221.2 {bar};

CASE 'oxygen':
T_c :== 154.6 {K};
p_c :== 50.4 {bar};

OTHERWISE:
T_c :== -1 {K};
p_c :== -1 {Pa};

END SELECT;
END eos_constants;</source>

In fact, this is the technique used in the current {{src|models/components.a4l}} model in our [[ModelLibrary]].

See also [[Conditional modelling]].

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