Units and dimensions

Schema against which LEMS based on these should be valid: LEMS_v0.7.6.xsd. Generated on 18/06/24 from this commit. Please file any issues or questions at the issue tracker here.

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Dimension

A Dimenson element associated a name with a particular combination of the standards SI base dimensions, mass, lenght, time, current, temperature and amount if substance (moles). Fractional dimensions are not currently supported.

Properties

name	String	The name to be used when referring to this dimension from variable declaration or units
m	int	Mass
l	int	Length
t	int	Time
i	int	Current
k	int	Temperature
n	int	Amount of substance
j	int	Luminous intensity

Schema

<xs:complexType name="Dimension">
  <xs:attribute name="name" type="xs:string" use="required"/>
  <xs:attribute name="m" type="xs:integer" use="optional" default="0"/>
  <xs:attribute name="l" type="xs:integer" use="optional" default="0"/>
  <xs:attribute name="t" type="xs:integer" use="optional" default="0"/>
  <xs:attribute name="i" type="xs:integer" use="optional" default="0"/>
  <xs:attribute name="k" type="xs:integer" use="optional" default="0"/>
  <xs:attribute name="n" type="xs:integer" use="optional" default="0"/>
</xs:complexType>

Usage: XML

<Dimension name="voltage" m="1" l="2" t="-3" i="-1"/>

<Dimension name="time" t="1"/>

<Dimension name="conductance" m="-1" l="-2" t="3" i="2"/>

<Dimension name="capacitance" m="-1" l="-2" t="4" i="2"/>

<Dimension name="current" i="1"/>

Unit

A Unit asociates a symbol with a dimension and a power of ten. For non-metric units a scale can be provided, as in ‘1 inch = 0.0254 m’. In this case there is a degeneracy between the power and the scale which is best resolved by not using the two together. The offset parameter is available for units which are not zero-offset, such as farenheit.

Properties

name	String	As with constants, units are only referred to within expressions using their symbols, so the name is just for readability.
symbol	String	The symbol is used to refer to this unit inside compound expressions coutaining a number and a unit symbol. Such expressions can only occur on the right hand side of assignments statements.
dimension	String	Reference to the dimension for this unit
power	int	Power of ten
scale	double	Scale, only to be used for scales which are not powers of ten
offset	double	Offset for non zero-offset units

Schema

<xs:complexType name="Unit">
  <xs:attribute name="symbol" type="xs:string" use="required"/>
  <xs:attribute name="dimension" type="xs:string" use="required"/>
  <xs:attribute name="power" type="xs:integer" use="optional" default="0">
    <xs:annotation>
      <xs:documentation>Some have asked whether fractional dimensions should be allowed. Disallowing it until needed...</xs:documentation>
    </xs:annotation>
  </xs:attribute>
  <xs:attribute name="scale" type="xs:float" use="optional" default="1"/>
  <xs:attribute name="offset" type="xs:float" use="optional" default="0"/>
</xs:complexType>

Usage: XML

<Unit symbol="mV" dimension="voltage" power="-3"/>

<Unit symbol="ms" dimension="time" power="-3"/>

<Unit symbol="pS" dimension="conductance" power="-12"/>

<Unit symbol="nS" dimension="conductance" power="-9"/>

<Unit symbol="uF" dimension="capacitance" power="-6"/>

Assertion

Assertions are not strictly part of the model, but can be included in a file as a consistency check.

Properties

dimension	String	The name of a dimension
matches	String	An expression involving dimensions. The dimensionality of the expression should match the dimensionality of the dimension reference.