Examples herein relate to hardware accelerators for calculating node values of neural networks. An example hardware accelerator may include a crossbar array programmed to calculate node values of a neural network and a current comparator to compare an output current from the crossbar array to a threshold current according to an update rule to generate new node values. The crossbar array has a plurality of row lines, a plurality of column lines, and a memory cell coupled between each unique combination of one row line and one column line, where the memory cells are programmed according to a weight matrix. The plurality of row lines are to receive an input vector of node values, and the plurality of column lines are to deliver an output current to be compared with the threshold current.