UNITS - Revision history

Jpye at 09:14, 3 March 2026

2026-03-03T09:14:39Z

← Older revision		Revision as of 09:14, 3 March 2026
Line 52:		Line 52:
	</source>		</source>

	== <tt>UNITS LADDER</tt>		== <tt>UNITS LADDER</tt> ==

	A new feature added (Feb 2026) is the <tt>UNITS LADDER</tt> statement. This allows new units to be defined while at the same time expressing a relationship between units in the same 'family' or 'ladder', like meters, kilometers, millimeters. This supports a new GTK GUI feature for 'auto-ranging units of measurement: a value like 0.1 MPa can be automatically re-scaled and displayed as 100 kPa instead. The GTK GUI provides new options to allow overrides for MODELs where a specific unit is desired for output.		A new feature added (Feb 2026) is the <tt>UNITS LADDER</tt> statement. This allows new units to be defined while at the same time expressing a relationship between units in the same 'family' or 'ladder', like meters, kilometers, millimeters. This supports a new GTK GUI feature for 'auto-ranging units of measurement: a value like 0.1 MPa can be automatically re-scaled and displayed as 100 kPa instead. The GTK GUI provides new options to allow overrides for MODELs where a specific unit is desired for output.

			From {{src\|models/measures.a4l}}:
			<source lang=a4c>
			UNITS LADDER
			nJ = {J*1.0e-9};
			uJ = {J*1.0e-6};
			mJ = {J*1.0e-3};
			J = {kg*m^2/s^2};
			kJ = {J*1000};
			MJ = {J*1e6};
			GJ = {J*1e9};
			TJ = {J*1e12};
			PJ = {J*1e15};
			END UNITS LADDER;
			</source>

	== See also ==		== See also ==

Jpye at 09:13, 3 March 2026

2026-03-03T09:13:27Z

← Older revision		Revision as of 09:13, 3 March 2026
Line 51:		Line 51:
	Q = 1{SIGMA_C} * A * T^4; (* radiant emissive power *)		Q = 1{SIGMA_C} * A * T^4; (* radiant emissive power *)
	</source>		</source>

			== <tt>UNITS LADDER</tt>

			A new feature added (Feb 2026) is the <tt>UNITS LADDER</tt> statement. This allows new units to be defined while at the same time expressing a relationship between units in the same 'family' or 'ladder', like meters, kilometers, millimeters. This supports a new GTK GUI feature for 'auto-ranging units of measurement: a value like 0.1 MPa can be automatically re-scaled and displayed as 100 kPa instead. The GTK GUI provides new options to allow overrides for MODELs where a specific unit is desired for output.

	== See also ==		== See also ==

Jpye at 19:01, 14 February 2012

2012-02-14T19:01:21Z

← Older revision		Revision as of 19:01, 14 February 2012
Line 29:		Line 29:

	Be careful to check the permitted units of measurement by search through the file {{src\|models/measures.a4l}}.		Be careful to check the permitted units of measurement by search through the file {{src\|models/measures.a4l}}.

			== Constants defined as UNITS ==

			ASCEND uses its units of measurement system to declare a number of commonly-used mathematical and physical constants, too. These are also declared in {{src\|models/measures.a4l}}. Examples are

			<source lang=a4c>
			PI= {3.1415926535897932385}; (* Circumference/Diameter ratio *)
			LIGHT_C = {2.99793e8 * m/s}; (* Speed of light in vacuum *)
			GAS_C = {BOLTZMAN_CAVOGADRO_C}; ( Gas constant *)
			SIGMA_C = {5.670e-8 * W/m^2/K^4 }; (* Stefan-Boltzmann constant for blackbody radiation *)
			EARTH_G = {9.80665 * m/s/s}; (* Earth's gravitational field, somewhere *)
			</source>

			The benefit of having these as units rather than as special constants is that you don't need to pollute your variable namespace with these things, and you can also conveniently write values such as

			<source lang=a4c>
			theta IS_A angle;
			theta = 0.75{PI*rad};

			Q IS_A energy_rate;
			Q = 1{SIGMA_C} * A * T^4; (* radiant emissive power *)
			</source>

	== See also ==		== See also ==

Jpye at 18:52, 14 February 2012

2012-02-14T18:52:31Z

← Older revision		Revision as of 18:52, 14 February 2012
Line 29:		Line 29:

	Be careful to check the permitted units of measurement by search through the file {{src\|models/measures.a4l}}.		Be careful to check the permitted units of measurement by search through the file {{src\|models/measures.a4l}}.

			== See also ==
			* [[Units of measurement]]
			* [[Dimensions]]
			* [[DIMENSION]]

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

Jpye: Created page with "The '''UNITS''' statement is used to declare new units of measurement derived from the other units, or from the base units that are predefined and associated with each of ..."

2012-02-14T18:51:22Z

Created page with "The '''UNITS''' statement is used to declare new units of measurement derived from the other units, or from the base units that are predefined and associated with each of ..."

New page

The '''UNITS''' statement is used to declare new [[units of measurement]] derived from the other units, or from the base units that are predefined and associated with each of the physcial [[dimensions]] supported in ASCEND.

ASCEND will recognize conversion factors when it sees them as {units}. These units are built up from the basic units,
and new units can be defined by the user. Note that the assignment <tt>x:= 0.5 {100}</tt> yields an <tt>x</tt> value of <tt>50</tt>, and that there is no support in ASCEND for 'offset conversions', such as conversions between Fahrenheit and Celsius (F=9/5*C+32). Please keep unit names to 20 characters or less, as this makes life pretty for other users.

One or more unit conversion factors can be defined with the UNITS keyword. A unit of measure, once defined, stays in the system until the system is shut
down. A measuring unit cannot be defined differently without first shutting down the system, but duplicate or equivalent definitions are quietly ignored.

A UNITS declaration can occur in a file by itself, inside a model or inside an atom. UNITS definitions are parsed immediately, they will be processed
even if a surrounding MODEL or ATOM definition is rejected. Because units and dimensionality are designed into the deepest levels of the system, a unit
definition must be parsed before any atoms or relations use that definition. It is good design practice to keep customized unit definitions in separate files
and REQUIRE those files at the beginning of any file that uses them. Unit definitions are made in the form, for example:

<source lang=a4c>
UNITS
(* several unit definitions are allow here. *)

(* derived SI units) *)
ohm = {kg*m^2/s^3/ampere^2};

(* alternative names *)
kilogram = {kg}

(* conversions and non-SI units *)
MW = {1e6*watt};
foot = {12*inch};
END UNITS;
</source>

Be careful to check the permitted units of measurement by search through the file {{src|models/measures.a4l}}.

[[Category:Syntax]]