# SpeciesVariables

Species in abstract kinetic law

## Description

This property shows species variables that are used in the `Expression` property of the kinetic law object to determine the `ReactionRate` equation in the reaction object. Use the function `set` to assign `SpeciesVariables` to an abstract kinetic law. For more information, see Kinetic Law Definition.

## Characteristics

 Applies to Objects: abstract kinetic law, kineticlaw Data type Cell array of character vectors Data values Defined by abstract kinetic law Access Read/write in abstract kinetic law. Read-only in kinetic law.

## Examples

### Define Michaelis Menten Reaction Kinetics in SimBiology Model

Create a SimBiology model with a reaction.

```m1 = sbiomodel("m1"); r1 = addreaction(m1,"A -> B");```

Add a kinetic law for the reaction by using the built-in kinetic law (Michaelis Menten). Check the expression of the kinetic law.

```kl = addkineticlaw(r1,"Henri-Michaelis-Menten"); kl.Expression```
```ans = 'Vm*S/(Km + S)' ```

Query the parameters and species variables defined in the kinetic law.

`kl.ParameterVariables`
```ans = 2x1 cell {'Vm'} {'Km'} ```
`kl.SpeciesVariables`
```ans = 1x1 cell array {'S'} ```

Define `Va` and `Ka` as `ParameterVariableNames`, which correspond to the `ParameterVariables` Vm and Km defined in the Expression property of the kinetic law. To set these variables, first create the parameter variables as parameter objects (p1, p2) with the names Va and Ka, and then add them to the kinetic law object kl. The species object with the name A is created when the reaction object r1 is created and need not be redefined.

```p1 = addparameter(kl,"Va"); p2 = addparameter(kl,"Ka");```

Set the variable names for the kinetic law object.

```kl.ParameterVariableNames = ["Va","Ka"]; kl.SpeciesVariableNames = ["A"];```

Verified that the reaction rate is expressed correctly in the `ReactionRate` property of the reaction object

`r1.ReactionRate`
```ans = 'Va*A/(Ka+A)' ```