Unable to append zeros to the vectors and matrices from within the member functions

Hi, I am trying to implement a class for a growing cylinderical organ,

objectibe: My constructor initiallizes the vectors and matrices whose sizes I want to increase with each iteration. This increase is size is achieved by calling growth function by appending zeros at the end of each vector and Matrix.

Issue: The problem is, I am unable to modify the size of the vectors and matrices from within the growth(obj) function. There is no errror, I even run my code step by step and check the size of my vectors at each iteration using size() command. The size remians the same as initialized, even though the growth(obj) function is successively called and run. I confirmed it by displaying messages from within the growth (obj) function at each iteration.

here is my code,

classdef Organ_Python
    %   Detailed explanation goes here
    
    properties
% % %             k1 =[];       %curvature
% % %             k2 =[];       %curvature
% % %             r  =[];       %centerline
% % %             D  =[];       %rotation matrices to centerline's local coordiates
% % %             NUM;          %Number of segments
% % %             NUM_gz;       %Number of segments in the growth-zone
% % %             ds;           %segment length
% % %             R;            %organ's radius
% % %             phi = [];
% % %             kappa = [];
% % %             B = [];
% % %             N = [];
                k1(1,:);       %curvature
                k2(1,:);       %curvature
                r (3,:);       %centerline
                D (3,:,3);       %rotation matrices to centerline's local coordiates
                NUM;          %Number of segments
                NUM_gz;       %Number of segments in the growth-zone
                ds;           %segment length
                R;            %organ's radius
                phi(1,:);
                kappa;
                B (3,:);
                N (3,:);
    end
    
    methods
        % constructor function to initialize vectors and matrices
        function organ = Organ_Python(NUM,NUM_gz,ds,R)      %Starts as a straight organ pointing to the z direction                     
            organ.k1 = zeros(1, NUM);        %curvature
            organ.k2 = zeros(1, NUM);        %curvature
            organ.phi = zeros(1, NUM);       %twist
            organ.kappa = zeros(1);          %curvature
            organ.r = zeros(3,NUM);          %centerline
            organ.B = zeros(3,NUM);            
            organ.N = zeros(3,NUM);            
            organ.D = zeros(3,NUM,3);          %rotation matrices to centerline's local coordiates
            organ.NUM = NUM;                   %Number of segments
            organ.NUM_gz = NUM_gz;             %Number of segments in the growth-zone
            organ.ds = ds;                     %segment length
            organ.R = R;                       %organ's radius
            %centerline initializtion:
            organ.D(:,1,:)=eye(3);
            organ.Update_centerline()
        end
        function growth(obj)   %increasing the length of the organ by one segment
            obj.k1= [obj.k1  0*ones(1)];
            obj.k2= [obj.k2  0*ones(1)];
            obj.phi=[obj.phi  0*ones(1)];
            obj.r = [obj.r  zeros(3,1)];
            obj.N = [obj.N  zeros(3,1)];
            obj.B = [obj.B  zeros(3,1)];
            obj.D = [obj.D  zeros(3,1,3)];
            %initializtion of the new segment:
            %U=organ.Darboux_Matrix(1);                                   %Darboux skew-symmetric matrix
            U = reshape(obj.D(:,end-1,:),[3,3])*reshape([[0,0,obj.k1(end-1)],[0,0,obj.k2(end-1)],[-obj.k1(end-1),-obj.k2(end-1),0]],[3,3])*(reshape(obj.D(:,end-1,:), [3,3]))';
            obj.D(:,end,:)=expm(obj.ds*U)*reshape(obj.D(:,end-1,:), [3,3]);     %Rotation of the local coordinates using the Rodrigues formula
            obj.r(:,end)=obj.r(:,end-1)+obj.ds*reshape(obj.D(2,end-1,:), [3,1]);             %centerline update
            obj.NUM=obj.NUM+1;     %increase number of segements
            obj.k1(end)=obj.k1(end-1);    %intializaing curvature
            obj.k2(end)=obj.k2(end-1);    %intializaing curvature
        end
    end
end

[per isakson]

See Comparison of Handle and Value Classes

Answer 1

[Matt J]

Either make your class a handle class

classdef Organ_Python<handle

or return a modified object from the growth() method

 function obj=growth(obj) 

Note that only with the first approach will you be able to have growth() cause in-place changes in your objects. With the latter method, you will only see the changes in the object returned as output from a call to growth().

[Abdul Jabbar]

@Matt J, Thank you very much for your help. I the tried first method ("classdef Organ_Python <handle") and it worked for me exactly as I wanted. I really appreciate your support.