How to break the iteration using an Error Equation

I have a 2D for loop iteration, I want to stop the iteration once change is less than a certain number! But I don't know how to recall the previous iteration?

Let's say equation is:

Iteration i=1:20000
x=function
y=function

result is A(x,y)

How to calculate change between the A at any i and i-1?

If I want the stop iterating (break the loop) when the change is <1 for example

I don't want to use A(x,y,i) code because my iteration sometimes stop changing at 20000 or so, that will require a huge memory

Thanks in advance

Answer 1

[Walter Roberson]

oldvalue = inf;

for i = 1 : 200000
  x = function
  y = function
  T = value that will go into A(x,y)
  A(x,y) = T;
  if abs(T - oldvalue) < Tolerance
    break
  end
  oldvalue = T;
end