Object array implemenation in MATLAB OOP

Suppose that we have this class in MATLAB R2014b :

classdef Pre

properties
    Value
end

methods
    function obj = Pre(F)

          if nargin ~= 0
              m = size(F,1);
              n = size(F,2);
              obj(m,n) = Pre;

              for i = 1:m
                  for j = 1:n
                      obj(i,j).Value = F(i,j);
                  end
              end
          end
      end
  end
  end

1) If we erase if nargin~=0 from this code we have this error :

Error using Pre (line 13)
Not enough input arguments.

Error in Pre (line 15)
                obj(m,n) = Pre;

Why? I think this is only checking for number of input arguments !

2) what is obj(m,n) = Pre;? what this line is doing in this code? This is for pre-allocating but how this line can do that?

I checked this class with this syntax: az = Pre([2 3 5;5 3 0])

Answer 1

[Geoff Hayes]

Jack - the error message, Not enough input arguments, makes sense since the code is calling the class constructor at the line

 obj(m,n) = Pre;

without any input arguments. So when the line

 m = size(F,1);

is executed, there is no F and the error appears. Try putting a breakpoint at this line, and then create an instance of this class to verify when this error is being generated.

As for what the line

 obj(m,n) = Pre;

is doing, it is just creating an mxn array of objects of the type Pre. This is typical MATLAB code where you want to initialize an array (or matrix) with an object of a data type. For example,

 array1(3,5) = uint8(0)

creates a 3x5 array of 8-bit unsigned integers, whereas

 array2(12,3) = single(0)

creates a 12x3 array of elements of the single data type.

[Jack]

Thank you for answer Geoff.