How to use for loop to set properties' attributes in MATLAB class?

I want to use the following loop to set properties' attributtes inside a class. Essentially it needs to store a struct as a class attribute. But when I put the following inside the class properties, its showing error.

            Total_Grids = 100; 
            Grid(Total_Grids) = struct();
            G = 1;
            for i = 1:this.XGrid
              for j = 1:this.YGrid
                  Grid(G).X = (this.GridSize/2)+ (j-1)*(this.GridSize); % x pos of each grid centre
                  Grid(G).Y = (this.GridSize/2)+ (i-1)*(this.GridSize); % y pos of each grid centre
                  G = G + 1;
              end
            end
            Profits = randi([0,20],100,1); % profit of each grid, 100 grids are there
            G = 1;
            for i = 1:Total_Grids
                Grid(G).Profit = Profits(G); % stored in Grid structure
                G = G+1;
            end

How and where to write it inside the class definition? I see normally the attributes are written like the following. Its not even using semicolon at the end of each attribute. How do I write a loop like the above here?

Thanks.

classdef CartPoleEnvironment < rl.env.MATLABEnvironment
    %CARTPOLEENVIRONMENT: Template for defining custom environment in MATLAB.    
    
    %% Properties (set properties' attributes accordingly)
    properties
        % Specify and initialize environment's necessary properties    
        % Acceleration due to gravity in m/s^2
        Gravity = 9.8
        
        % Mass of the cart
        CartMass = 1.0
        
        %....and so on
    end

[Steven Lord]

What is the full and exact text of the error message you receive? Please show all the text displayed in red and/or orange when you try to run the property setting code.

[laha_M]

This is how I have written

 properties
        Total_Grids = 100; %this.XGrid*this.YGrid;
            Grid(Total_Grids) = struct();
            G = 1;
            for i = 1:10
              for j = 1:10
                  Grid(G).X = (this.GridSize/2)+ (j-1)*(this.GridSize); % x pos of each grid centre
                  Grid(G).Y = (this.GridSize/2)+ (i-1)*(this.GridSize); % y pos of each grid centre
                  G = G + 1;
              end
            end
            Profits = randi([0,20],100,1); % profit of each grid, 100 grids are there
   
            for i = 1:Total_Grids
                Grid(G).Profit = Profits(G); % stored in Grid structure
                G = G+1;
            end
            end
            

For which I get the following error:

Illegal use of reserved keyword

"for".

I am attaching one screenshot. Seems such syntax is not allowed.

[laha_M]

I understand that there was one confusing part because I was using 'this.something' even before creating the object.

But when I remove them and implement the for loop like this (without using any 'this')

for i = 1:10
              for j = 1:10
                  Grid(G).X = 10 + (j-1)*20; % x pos of each grid centre
                  Grid(G).Y = 10+ (i-1)*20; % y pos of each grid centre
                  G = G + 1;
              end
            end

I get the same error and warnings.

Thanks.

Answer 1

[Matt J]

You cannot put a for loop or other complex code inside a properties block. If you wish, you can set a default value for a property with the following function call syntax, as long as the function defaultProp1() requires no inputs. Otherwise, you must initialize the property in the constructor.

classdef myclass
    properties
        prop1=defaultProp1()
   end
  


end

function value=defaultProp1()

  ...

end

Here defaultProp1() can be defined anywhere that is visible to the classdef file, but a good place to put it would be in the classdef file as a class-related function.

[laha_M]

Thanks. I have used the function method. It worked.

Interested to know about 'you must initialize the property in the constructor' part. Any documentation/examples?

[Matt J]

Of course!

https://www.mathworks.com/help/matlab/matlab_oop/create-a-simple-class.html#buoz_mi

https://www.mathworks.com/help/matlab/matlab_oop/class-constructor-methods.html

[laha_M]

Thanks.