When to reach pure PoS?

[quote=“singlethread, post:1, topic:361”]I wonder why the ratio between number of proof-of-work blocks and proof-of-stake blocks is variable in PPC.

The PPC paper does not say much about it. I see in the source code that the PoW difficulty is pushed up when the combined block spacing of PoW and PoS is less than 10 minutes, and difficulty is pushed down whenever PoW+PoS spacing is more than 10 minutes or PoW spacing is more than 120 minutes. As a result, PoW difficulty depends not just on PoW hashrate but also on perturbations in PoS block spacing.

It seems to me that this free floating PoW/PoS ratio makes it very difficult for PoW miners to predict how much PPC they will get for their investment. Even when PoW hash rate is steady or steadily rising, the PoW difficulty will still bounce up and down. Indeed, looking at PoW difficulty vs hash rate over the past months shows an almost negative correlation. (This post may seem to be more about PoW than PoS, but I think it is very much related.)

Can someone explain the function of variable PoW spacing?
Was this done deliberately and what goal does it accomplish?[/quote]

Given the situation, I am wondering when can we see a pure PoS network?