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Specify variable or constant parameter value


The ConstantValue property indicates whether the value of a parameter can change during a simulation. Enter either true (value is constant) or false (value can change).

You can allow the value of the parameter to change during a simulation by specifying a rule that changes the Value property of the parameter object.

The property ConstantValue is for parameter objects; the property ConstantAmount is for species objects.

More Information

As an example, consider feedback inhibition of an enzyme such as aspartate kinase by threonine. Aspartate kinase has three isozymes that are independently inhibited by the products of downstream reactions (threonine, homoserine, and lysine). Although threonine is made through a series of reactions in the synthesis pathway, for illustration, the reactions are simplified as follows:

Aspartic acid aspartate kinaseβAspartylphosphateβAspartylphosphate Threonine

To model inhibition of aspartate kinase by threonine, you could use a rule like the algebraic rule below to vary the rate of the above reaction and simulate inhibition. In the rule, the rate constant for the above reaction is denoted by k_aspartate_kinase and the quantity of threonine is threonine.

 k_aspartate_kinase -(1/threonine)


Applies toObject: parameter
Data typeboolean
Data valuestrue or false. The default value is 'true'.


  1. Create a model object.

    modelObj = sbiomodel ('my_model');
  2. Add a parameter object.

    parameterObj = addparameter (modelObj, 'kf');
  3. Change the ConstantValue property of the parameter object from default (true) to false and verify.

    MATLAB® returns 1 for true and 0 for false.

    set (parameterObj, 'ConstantValue', false);
    get(parameterObj, 'ConstantValue')

    MATLAB returns:

    ans =

See Also