Sunday, March 18, 2012

oscillate, explode, or stabilize

must learn about runge-kutta methods,
must learn about runge-kutta methods,
must learn about runge-kutta methods.

clearly this too-complicated model is suffering because of the temporal resolution. i've spent nights now trying to figure out why the thing wasn't working right - and did find a few errors along the way, which i don't think would have made or brake the thing anyways - and finally i conclude that the response time constant was too small. this is strange, because the same model works great with a 2d network, and perfect with a single unit; apparently there's something about this network, which is essentially 3d, which effectively makes the time constants faster... it must be that compounding the differential during the convolution, over multiple filter layers, effectively speeds everything up.

it's not like i wasn't aware of this problem at first. i thought i had solved that by doing the global normalization, where the convolution stage would basically be treated as a single layer. last night, i decided that collapsing that stage to one layer was a mistake, because it resulted in the pools everywhere being overwhelmed by the finer-grain channels, since those filters are more numerous. that may actually be correct, with some sort of leveling factor, but at any rate i took out the collapse. it didn't change performance much, but that's when i was using a too-complex test case (two faces), instead of the current test case of two gratings. now i realize that the pooling was accelerating the responses, resulting in useless behavior by the network - turning up the interocular inhibition to any level that did anything tended to result in ms-to-ms oscillations.

so, the compounding of responses was doing it, i guess, and would be doing it even if i had the pooling collapse still worked in. but now i can't understand why i didn't get the same problem, apparently ever, with the fft-based version of the model. now i'm suspicious that maybe i *did* get it, and just never perceived it because i wasn't doing the same sorts of tests with that thing.

not quite back to the drawing board. i wish i could get away from the drawing board, for just a few nights, so i could work on this goddam proposal like i should have been doing for the past 2 months.

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