DIMENSION - Revision history

Jpye at 18:42, 14 February 2012

2012-02-14T18:42:14Z

← Older revision		Revision as of 18:42, 14 February 2012
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	Real values have '''dimensionality''' such as length/time for velocity. Dimensionality is to be distinguished from the units such as km/h or ft/s. ASCEND takes care of mapping between units and dimensions. A value without units (this includes integer values) is taken to be dimensionless. Dimensionality is built up from the following base dimensions:		The '''DIMENSION''' keyword is encountered in the [[ATOM]] and [[CONSTANT]] declarations in ASCEND syntax. It is used to declare the dimension that a particular variable or constant will be required to take.

			Real values have '''dimensionality''' such as length/time for velocity. Dimensionality is to be distinguished from the [[units]] such as km/h or ft/s. ASCEND takes care of mapping between units and dimensions. Many different measurement units may exist for a variable of any given dimensionality. A value without units (this includes integer values) is taken to be dimensionless. Dimensionality is built up from the following base dimensions:

	{\| class='wikitable'		{\| class='wikitable'

Jpye at 18:37, 14 February 2012

2012-02-14T18:37:39Z

← Older revision		Revision as of 18:37, 14 February 2012
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	{{~~missing}~~}		Real values have '''dimensionality''' such as length/time for velocity. Dimensionality is to be distinguished from the units such as km/h or ft/s. ASCEND takes care of mapping between units and dimensions. A value without units (this includes integer values) is taken to be dimensionless. Dimensionality is built up from the following base dimensions:

			{\| class='wikitable'
			! Symbol \|\| definition !! typical units !! symbol
			\|-
			\| L \|\| length \|\| metre \|\| m
			\|-
			\| M \|\| mass \|\| kilogram \|\| kg
			\|-
			\| T \|\| time \|\| second \|\| s
			\|-
			\| E \|\| electric current \|\| ampere \|\| A
			\|-
			\| Q \|\| quantity \|\| mole \|\| mol
			\|-
			\| TMP \|\| temperature \|\| kelvin \|\| K
			\|-
			\| LUM \|\| luminous intensity \|\| candela \|\| cd
			\|-
			\| P \|\| plane angle \|\| radian \|\| rad
			\|-
			\| S \|\| solid angle \|\| steradian \|\| srad
			\|-
			\| C \|\| currency \|\| US dollars \|\| USD
			\|}

			The [[ATOM]] and [[CONSTANT]] definitions in the library illustrate the use of dimensionality. Dimensions may be any combination of these symbols along with rounded parentheses, (), and the operators , ^ and /. Examples include <tt>M/T</tt> or <tt>ML^2/T^2/TMP</tt> (this latter means <tt>(M*(L^2)/(T^2))/TMP</tt>). The second operand for the to-the-power-of operator, ^, must be an integer value (e.g., -2 or 3) because fractional powers of dimensional numbers are physically undefined in ASCEND. If the dimensionality for a real value is undefined, then ASCEND gives it a wildcard dimensionality. If ASCEND can later deduce its dimensionality from its use in a model definition it will do so. For example consider the real variable
			a, suppose a has wildcard dimensionality, b has dimensionality of L/T. Then
			the statement

			<source lang=a4c>
			a + b = 3 {ft/s};
			</source>

			requires that a have the same dimensionality as the other two terms, namely, <tt>L/T</tt>. ASCEND will assign this dimensionality to <tt>a</tt>. The user will be warned of dimensionally inconsistent equations.

			== See also ==
			* [[Units]]
			* [[ATOM]]
			* [[CONSTANT]]

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

Jpye: Created page with '{{missing}} Category:Syntax'

2010-05-17T03:28:57Z

Created page with '{{missing}} Category:Syntax'

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