Section: Object Oriented Programming
mat object 
function p = mat(a)
  if (nargin == 0)
    p.c = [];
    p = class(p,'mat');
  elseif isa(a,'mat')
    p = a;
  else
    p.c = a;
    p = class(p,'mat');
  end
Generally speaking when it is provided with zero arguments, the constructor returns a default version of the class using a template structure with the right fields populated with default values. If the constructor is given a single argument that matches the class we are trying to construct, the constructor passes through the argument. This form of the constructor is used for type conversion. In particular,
p = mat(a)
guarantees that p is an array of class mat.  The last form
of the constructor builds a class object given the input.  The
meaning of this form depends on what makes sense for your class.
For example, for a polynomial class, you may want to pass in the
coefficients of the polynomial.