1. A physical neural network comprising: a dendrite circuit comprising two two-terminal non-volatile nanotube switches, wherein: the first and second terminals of each non-volatile switch are in contact with opposite ends of a patterned non-woven nanotube fabric; the second terminal of the first non-volatile nanotube switch and the second terminal of the second non-volatile nanotube switch share a common node; and the common node sums any input signals at the first terminals of the non-volatile switches.