The SP output can possibly produce 1 billion+ different patterns but that is what I would consider its "resolution", not its "capacity" or "accuracy" which is what we're after in this thread and what is the desirable property that one seeks to evaluate and optimize. A completely unlearned SP will also produce 1 billion+ different output patterns so that can't possibly be an interesting property.Sorry what value can be 1 billion? You keep bringing up that number. No spatial pooler of any sane dimensions has a capacity of 1 billion. Not for any reasonable definition of "capacity".In this case we are just trying to discriminate between a fixed set of patterns. By "discriminate" we mean the SDR output should be unique with respect to the other patterns by at least one winning column. Since there are 1024 columns, of which 64 are on at a time, the total number of patterns that can be discriminated is 1024 choose 64 > 10^102. In reality it will be less than that, but if two inputs differ by more than a few bits, we will have at least one column that is different. As such, there is quite a bit of room here.
A real-world analogy: The local jeweler weighs precious metals with scales boasting a resolution of .01g but in the interest of getting a fair deal on my silver I'd rather know their accuracy. Scales with a resolution of .01g can still be off by 5g and usually will be so straight off the assembly line so they have to be calibrated, a primitive material world version of "learning".
Or your digital SLR camera + computer monitor boast a 24bit color depth allowing for 4 million+ colors but that's saying nothing about how faithfully they reproduce the exact shade of red of a flower that you photographed and there's a calibration/"learning" process too that involves photographing known colors off a pantone sheet.
A good definition of SP capacity or accuracy would IMHO involve a correlation between inputs and ouputs, along the lines of how well clusters in the input vector space correlate to clusters in the output vector space. Just thinking out loud here.
-- Rik
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