There are certainly plenty of firms that use AI-based investing techniques, but my understanding is that after being fashionable in the late 90s, they've fallen

There are certainly plenty of firms that use AI-based investing techniques, but my understanding is that after being fashionable in the late 90s, they've fallen out of favor. After a couple AI-based systems "blew up," people realized that they're essentially opaque: you can't look at a neural network or a genetic algorithm and realize precisely what went wrong and fix it for next time. There's nowhere to place the blame -- not even on the programmer, since he didn't directly create the trading rules.