How to make smaller numbers give more points?

Question

PHP

I subtract the posting time for the present (example: 1493490780-1493487180) and I need to sort by the most relevant posts, I can do this, but I need to make points according to the "less is better" algorithm,
subtraction gives equality, for example ,
up to 3600 then points will be 50000
from 3601 to 7200 points 25000
from 7201 to 10800 points 10000

Answer 1

Literally, your rules are implemented by similar JavaScript code - with conditions:

function getPostScore(time) {
  var diff = Math.floor((new Date()).getTime()/1000) - time;
  if( diff <= 3600) return 50000;
  else if( diff <= 7200) return 25000;
  else if( diff <= 10800) return 10000;
  else return 0;
}

getPostScore(1493487180); // 10000

But the stepping of values ​​is probably not fully justified and it would be better to have some kind of smooth function. For example, of the type y = k / x
With a coefficient k = 50000 * 3600, it successfully captures the second point as well. But it is bad because closer to zero it goes off scale to + infinity.
Probably, for your task, an S-shaped curve is more appropriate - sigmoid , given by a formula like y \u003d 1 / (1 + e ^-x ) Approximately picked up the coefficients:

function getPostSigma(time){
  var diff = Math.floor((new Date()).getTime()/1000) - time;
  return Math.round( 10000 + 40000 / (1 + Math.exp((diff-6800)/700)));
}

getPostSigma(1493531780); // 49998
getPostSigma(1493522780); // 11545

Answer 2

HIGHEST*exp(-diff/SPEED)
where
HIGHEST is the maximum points value constant (for placement 0 seconds ago)
SPEED is the rate of decrease constant
e.g.
50000*exp(-diff/4500)