Object composition and updating property

I'm writing my first program with the OOP method during several weeks and i face with an issue with composition object and update properties of object . Here is the definition of my classes: First the class Mat:

 classdef Mat < handle

    properties
        z_left
        z_right
        dz
    end

    properties(Dependent)
        z
    end

    methods 
        % Constructor
        function newMat = Mat(z_left, z_right, dz)
            if nargin == 3
                newMat.z_left = z_left;
                newMat.z_right = z_right;
                newMat.dz = dz;
            end
        end

        function z = get.z(newMat)
            z = (newMat.z_left:newMat.dz:newMat.z_right)';
        end

        function newMat = set.z_left(newMat,value)
            newMat.z_left = value;
        end

    end

 end

I use a function sysmeca to create an object composed of two instanciation of the class Mat:

function [ obj ] = Sysmeca( varargin )

    if (nargin < 1), error('Wrong number of input arguments.'); end
    %
    n = length(varargin);
    obj = cell(1,n);
    for k=1:n
      obj{k}=varargin{k};
    end

end

Then the class Model:

classdef Model < handle
    properties
        obj;
    end
    properties(Dependent)
        z
    end
    methods

          function newModel = Model(obj)
              newModel.obj = obj;
          end

          function z = get.z(newModel)
              L = 0;
              z = 0;
              for k=1:length(newModel.obj)
                  z = [z ; newModel.obj{k}.z + L];
                  newModel.obj{k}.z_left = L;
                  L = newModel.obj{k}.z_left;
              end
          end

      end
   end

Here is finally the main script:

clc;
close all;
clear all;
clear classes;

cm = 1e-02;
Mat1 = Mat(0,5*cm,0.1*cm);
Mat2 = Mat(0,2*cm,0.2*cm);
sys = Sysmeca(Mat1,Mat2);
Part = Model(sys);

My problem is that i wish to update property z_left in the objects Mat1 and Mat2 inside the get.z method in the class Model by the instruction newModel.obj{k}.z_left = L;, but it doesn't work. I try to implement a set method in the class Mat definition to update the property z_left, but no success.

Can somebody help me to understand how i can update property object which is part of an object composition ?? Thanks a lot in advance.

[Matt J]

Works fine for me. I get no error messages with or without the explicitly defined set.z_left (which looks unnecessary).