E0101: LIF tau_mem too small for effective dt
What happened
The compiler’s validate pass found a LIF layer where tau_mem ≤ dt. This makes the leak factor alpha = exp(-dt / tau_mem) approach zero — the neuron would forget its entire state within one timestep.
Why
The membrane time constant (tau_mem) controls how long a neuron remembers its history. If tau_mem ≤ dt, the neuron has no memory — it resets completely every step, which is equivalent to a threshold gate, not an integrator.
This guard implements ADR-0005: the discretization must preserve the membrane dynamics in a physically meaningful way.
How to fix
- Increase
tau_mem: set tau_mem to a value clearly greater than dt. For dt=1.0ms, a tau_mem of 5ms or more is reasonable.
- Reduce
dt: if your application requires very fast membrane dynamics, reduce the simulation timestep. dt=0.1ms with tau_mem=0.5ms is valid.
- If you are targeting hardware with a larger native
dt (e.g. 2ms), the retiming pass will also raise E0101 if the effective tau_mem is too small for the target’s dt.
Example
Physical interpretation
alpha = exp(-dt/tau_mem). For tau_mem = dt: alpha = exp(-1) ≈ 0.368. For tau_mem = dt/2: alpha ≈ 0.135. The guard fires when tau_mem ≤ dt, ensuring at least alpha > 1/e ≈ 0.368.
