Structures are used to store structural data.
e.g. struct(a,1,b,2) will create a structure with two fields called
a and b which are assigned the values 2 and 4
If the first element is a variable storing a structure then the new structure
will contain it's fields.
x = struct(a, 1, b, 2)
a = 1 : b = 2 :
y = struct(x, c, 3)
a = 1 : b = 2 : c = 3 :