If-else decision structure using op amps or any other non-programmable electronic device
Analog computers


Analog computers can do much of what you want to do.  Essentially, they consist of analog block functions that you can assemble as needed like building blocks, and twiddle knobs to tweak parameters.  Some had comparators, which you would use to drive yes/no decisions based on the resulting analog signals.  I've seen these beasts, which are things of the past, used to estimate parameters in differential equations.  Some had essentially swappable breadboards, which let you change simulations easily.  I don't believe you can still buy analog computers, but if you know what your morphology will be, you can certainly build the equivalent with op-amps and passives. This may be within your reach if your equations are simple enough (though I don't know the algorithm you would use to take on the problem you describe).

http://www.analogmuseum.org/english/impressions/eai_tr48.jpg


  Neuromorphic circuits/Neural Networks


Another strategy is to use MANY stereotypical nonlinear analog building blocks, connect them in strange ways, and let complicated algorithms tweak the weights of connections between the hundreds to thousands of elements.  This is called neural computing.  The theories are analog, but most are digitally implemented.  There are some custom made integrated circuits (some used to be commercially available, some may still be) that actually do analog implementations.  Just last week, I saw video of a neuromorphic CCD that was exquisite at sensing image motion.  There are academic journals, like Neural Computation, dedicated to these pursuits.

This approach is likely beyond what you want to implement. 

http://lowercolumbia.edu/facultyResource-crhode/NNimages/NasaNeuralNetwork.jpg