Flag to perform unit conversion for a SimBiology model before simulation, specified
as numeric or logical 1 (true) or 0
(false).
When UnitConversion is set to true, SimBiology
converts the matching physical quantities to one consistent unit system in order to
resolve them. This conversion is in preparation for correct simulation, but species
amounts are returned in the user-specified units.
For example, consider a reaction a + b —> c. Using mass
action kinetics the reaction rate is defined as a*b*k where
k is the rate constant of the reaction. If you specify that initial
amounts of a and b are 0.01M and 0.005M
respectively, then units of k are 1/(M*second). If
you specify k with another equivalent unit definition, for example,
1/((molecules/liter)*second), UnitConversion
occurs after DimensionalAnalysis.
Unit conversion requires dimensional analysis. If
DimensionalAnalysis is off, and you turn
UnitConversion on, then DimensionalAnalysis is
turned on automatically. If UnitConversion is on and you turn off
DimensionalAnalysis, then UnitConversion is
turned off automatically.
If UnitConversion fails, then you see an error when you
simulate.
If UnitConversion is set to false, the
simulation uses the given object values.
Note
SimBiology uses units including empty units in association with DimensionalAnalysis and UnitConversion features.
When DimensionalAnalysis and
UnitConversion are both false, units are
not used. However, SimBiology still performs a minimum level of dimensional analysis to decide
whether a reaction rate is in dimensions of amount/time or
concentration/time.
When DimensionalAnalysis is true and
UnitConversion is false, units (if not
empty) must have consistent dimensions so that SimBiology can perform dimensional analysis. However, the units are not
converted.
When UnitConversion is set to true
(which requires DimensionalAnalysis to be
true), SimBiology performs a dimensional analysis and
converts everything to consistent units. Hence, you must specify consistent units,
and no units can be empty. If you have a dimensionless parameter, you must still
set its unit to dimensionless.
SimBiology allows exponentiation of any dimensionless quantity to any
dimensionless power. For example, you can write the following expression if both
x and a are dimensionless: (x +
3)^(a + 0.5)
Tip
If you have a custom function and UnitConversion is on, follow the recommendation below.
Non-dimensionalize the parameters that are passed
to the function if they are not already dimensionless.
Suppose you have a custom function defined as y = f(t) where t is
the time in hour and y is the concentration of
a species in mole/liter. When you use this function in your model
to define a repeated assignment rule for instance, define it as: s1
= f(time/t0)*s0, where time is the simulation
time, t0 is a parameter defined as 1.0 hour, s0 is
a parameter defined as 1.0 mole/liter, and s1 is
the concentration of a species in mole/liter. Note that time and s1 do
not have to be in the same units as t0 and s0,
but they must be dimensionally consistent. For example, the time and s1 units
can be set to minute and picomole/liter, respectively.
Data Types: double | logical
