Units and dimensions

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.

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.

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

 
<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>

<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.

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

 
<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>

<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.

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.
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