StateVectors are vector objects similar to GSL vector types which store floating point numbers. In Auryn they are used in a NeuronGroup to store the state of all neurons and Auryn implements functions to monitor them or to save and load them to/from disc. Typically each neuron model will at least have one such vector storing the membrane potential. SpikingGroup implements a set of generic mechanism to create or retrieve such vectors. The probably most useful one is

auryn_vector_float * get_state_vector(string key);

which will return a StateVector corresponding to its key or specifier. For instance mem is the default specifier for the membrane potential. Note, that get_state_vector should typically only be called during initialization of a group and not in the evolve method of any NeuronGroup, because the call is relatively costly.