function ewma(alpha, f, from, to, by) {
// XXX Yuck
if (! f._ewma_cache_id) {
f._ewma_cache_id = EWMA_CacheID++;
}
var key = f._ewma_cache_id +
'-alpha-' + alpha +
'-to-' + to.milliseconds() +
'-by-' + by.milliseconds();
var result = EWMACache.get(key);
if (result !== null) {
return result;
}
// commented out the block below because the difference between
// cached versus computed values was leading to erratic ripple
// behavior. revisit this optimization later.
//
// // Check if we are computing one step past a previously-calculated ewma.
// // If so, use the previous calculation to get us one step closer.
// var prev = f._ewma_cache_id +
// '-alpha-' + alpha +
// '-to-' + to.subtract(by).milliseconds() +
// '-by-' + by.milliseconds();
// result = EWMACache.get(prev);
// if (result) {
// result = (1 - alpha) * result + alpha * f(to);
// } else {
// result = _ewma(alpha, f, from, to, by);
// }
result = _ewma(alpha, f, from, to, by);
EWMACache.put(key, result);
return result;
}
function latent(moment) {
var key = latent_stoke.seed + '-' + latent_stoke.dt + '-' + moment.milliseconds();
var result = LatentMetricCache.get(key);
if (result === null) {
result = _latent(moment);
LatentMetricCache.put(key, result);
}
return result;
}