Why is this opencl code non-deterministic?

You are running WIDTH x HEIGHT work-items. For each value of X in your kernel, there will be WIDTH work-items doing exactly the same thing in parallel: setting CX to 0, and then updating it in the Y loop. All these WIDTH work-items will read CX and then update it more or less at the same time.

This "more or less" is the cause of the variations you observe.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.