heun object

(Shortest import: from brian2 import heun)

brian2.stateupdaters.explicit.heun = ExplicitStateUpdater('''__x_support = __dW*__g(__x, __t) + __x __g_support = __g(__x_support, __t + dt) x_new = 0.5*__dW*(__g_support + __g(__x, __t)) + __x + dt*__f(__x, __t)''', stochastic='multiplicative')

Stochastic Heun method (for multiplicative Stratonovic SDEs with non-diagonal diffusion matrix)