I'm not sure if a user defined MATLAB function is executing or not in Simulink.

To demonstrate the error, I am running a stripped down version of a neuron firing. Essentially, the variable v obeys the equation:

An image of the simulink model:

where I, the current, is just a square wave. Initially, and . When , becomes positive and v starts rising. In the simulink model a function "spike_checker" has been defined which makes flag = 1 every time v crosses 0.5 (a "threshold", lets say).

This value of the flag is used to trigger the integrator to reset the value of v back to zero (a "rising edge" on the flag variable resets the integrator). Now, the integrator is getting reset just as expected, but the problem is, when I see the value of "flag" on the scope, it shows that flag = 0 throughout. It never becomes 1.

But, it must become 1, or else what is triggering the integrator to reset?

I've attached the Simulink model file, and an image of the simulink model, as well as an image of the scope output.

So, the question is, why is the flag variable never becoming 1, yet the integrator is resetting the value of v?

[Midhulesh Vellanki]

I ran the model, v never croses 0.5. It might help to use the zoom tool to see the value closely.

Tip: you can put breakpoints in the matlab function for debugging purposes.

Answer 1

[Paul]

Consider replacing the threshold crossing detection functionality in spike_checker with a self resetting integrator. Feed the state port into a Compare to Constant block, which then feeds the reset port.