I found that another user (hh_algos) with rating 2149 and rank 65 is expected to gain 134 points while i, with rating 2141 and rank 58, will gain 94 points.

I’m neither accusing anyone nor blaming, but was interested to know whether the predictor is working correctly or not…

Because a person with better rank and similar ratings ought to gain more.

I have read the codechef ratings page but it didn’t helped me much understanding this strange rating prediction

There is a concept called “volatility” used by codechef, which is in play here. Like in probability, we express “Expected value and variance”. Volatility corresponds to variance, or in other words, “How sure are we that he will be able to get the expected rank.”

Of course, if we arent sure about that, then him getting expected rank should lead to a bigger increase in rating (and our expectation next time :3). This was the reason I suffered a ~80 loss of rating in lunchtime despite <200 rank.

Further, I think it was made by a friendly user of our community, not codechef, so I am not sure if @admin can do anything about it.

And about users getting lucky contest, surely that particular user isn’t bound to get lucky again and thus, will reach the level, their skills actually are after next contest

it is to accelerate the convergence to the 'correct' rating. So when a person starts out, her volatility will be high, so that if she's like petr, her rating can jump up a lot in the first few contests itself. And then it tends to stabilize.