How can I make a sum of two numbers update if one of the terms is updated in MATLAB 7.9 (R2009b)?

I have calculated a sum of 2 numbers - a and b:

a=3;

b=3;

c=a+b;

I then modify a and would like c to update:

a=4;

c

However, c remains the same, as a, b, and c are of class double which is a value class. How can I write a custom handle class that would implement this functionality?

Answer 1

[MathWorks Support Team]

Define a custom class MYDOUBLE as follows:

classdef mydouble<handle

      properties(SetObservable)

          value

      end

      methods

          function obj=mydouble(v)

              obj.value=v;

          end

          function update(obj,src,event,c,b)

              c.value= obj.value+b.value;

          end

      end

end

You can then use the following code to update the value of the sum of two numbers:

clear classes

%create 3 mydouble. the 3rd one will be the sum of the first two

a = mydouble(5);

b = mydouble(4);

c = mydouble(a.value+b.value);

% add listeners to objects a and b so that they could listen for the change in their % property 'value' and update the sum c

addlistener(a,'value','PostSet',@(src, event) a.update(src, event,c, b));

addlistener(b,'value','PostSet',@(src, event) b.update(src, event,c, a));

% test the update

c.value

 ans = 

        9

a.value = 15;

c.value

 ans = 

       19

b.value = 30;

c.value

 ans =

        45

Please refer to the documentation for more information on Defining Events and Listeners:

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