Cannot find 'set' method for .... class

Matlab complains about a set method that has already been defined. The error message is, when I type in the command:

set(a, 'prop1', 1)

"Error using set. Cannot find 'set' method for aSimpleValueClass class".

 classdef aSimpleValueClass

    properties
        prop1
    end

    methods
        function obj = set.prop1(obj, x)
            obj.prop1 = x;
        end
    end

 end

Can someone tell me why?

Answer 1

[Walter Roberson]

You would need to have defined a method named set for that case. The set.prop1 method is called for the case where you use

a.prop1 = value

[Yves]

I thought (in the body of my classdef)

 function obj = set.prop1(obj, value)
 end

IS my set method, according to the OOP manual and examples.

[per isakson]

See matlab.mixin.SetGet class

[Walter Roberson]

When I look at the documentation, it appears to me you would need a method named just set in order to use set() as a call.

[Yves]

Somehow I thought my syntax was correct based on this manual page (please click on the hyperlink):

Property Set Methods

The set method has a difference, I noticed though from the manual, between a value class and a handle class: "Value class set functions must return the modified object to the calling function. Handle classes do not need to return the modified object." However, I re-typed

a = set(a, 'prop1', 3.0);

did not make the error message go away.

[per isakson]

This is a better reference: Implement Set/Get Interface for Properties

[Guillaume]

@Yves, no, you misunderstood. A property set method is used when you want to override what happens when you do

obj.property = value;

and it only works when you use that syntax. If you want to be able to set or get property with a generic set or get function, as works for graphics objects, you need to derive from matlab.mixin.SetGet which will automatically provide these methods. Note that matlab.mixin.SetGet forces your class to be a handle class, so the syntax would have to be

set(a, 'prop1', 3.0);

If you want do have a value class and a generic set method you'll have to write it yourself. The function will be defined as

methods 
    function obj = set(obj, property, value)
       %code to set property, eg:
       if isprop(obj, property)
         obj.(property) = value;
       end
    end
end

The above function would still live alongside the set.prop1 function if you want to override what happens when assigning to prop1 (e.g. validate inputs)

[Yves]

Ahh...I see. Thx, Guillaume.

[Giuseppe Degan Di Dieco]

Also, thanks by me!

Best!

Answer 2

[sneha pc]

error- set is not comaptable with sym class. what to do

M = 0.5;

m = 0.2;

b = 0.1;

I = 0.006;

g = 9.8;

l = 0.3;

q = (M+m)*(I+m*l^2)-(m*l)^2;

syms s

Ppend=((m*l*s^2)/q)/(s^4+(b*(I+m*l^2)*s^3)/q-((M+m)*m*g*l*s^2)/q-(b*m*g*l*s)/q);

disp(Ppend);

Pcart=(((I+m*l^2)*s^2-g*m*l)/q)/(s^4+(b*(I+m*l^2)*s^3)/q-((M+m)*m*g*l*s^2)/q-(b*m*g*l*s)/q);

disp(Pcart)

sys_tf = [P_cart ; P_pend];

inputs = {'u'};

outputs = {'x'; 'phi'};

set(sys_tf,'InputName',inputs)

set(sys_tf,'OutputName',outputs)

sys_tf;

Answer 3

[Walter Roberson]

You created a symbolic expression that looks like a transfer function, and you are expecting that it is suddenly the transfer function datatype instead of being symbolic.

You should use the routine in this link:

https://www.mathworks.com/matlabcentral/mlc-downloads/downloads/submissions/26553/versions/2/previews/sym2tf.m/index.html