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Stefano Bettani
@ginkobab
Hello, is somebody here?
Stefano Bettani
@ginkobab

Well I'll just leave this here: I'm trying to implement in DiffEq the update rule for a spiking neural network. For now I've implemented with plain Julia and works decently, but I'd like to speed it up a little:

The function simulate just initialize the variables and then runs step! for 10000 times.

The function step! takes as input:
V: a matrix(neurons x time), where values are potentials of individual neurons at a certain time
sd: a vector(neurons), where values represent how long ago a given neuron spiked
w: a matrix(neurons x neurons) of weights (connectivity matrix)
np, ep are parameters
tottime is the total time of simulation

function simulate(tottime, np, sp, ep)
    w = genweights(np, sp)
        V = zeros(np.N, tottime)
        sd = zeros(np.N) .+ 0.2

    V[:, 1:4] .= np.Vᵣ
    V[126:132,1:4] .= 0.

    for t in 3:tottime-1
        step!(V, sd, t, w, np, ep, tottime)
    end

    V[:, 1:tottime], sd
end


function step!(V, sd, t, w, np, ep, tottime)

    V[:, t+1] = dv(view(V, :, t), sd, w, np, ep) # This is the update
    V[view(V,:, t) .> np.Vₜ, t+1] .= 0.0  # This makes the neurons over the threshold spike
    V[view(V,:, t) .== 0.0, t+1] .= np.Vᵣ  # This reset the neurons that spiked to a low potential 

    sd .+= ep.dt  # Here we adjust the spike delays for the next timestep
    sd[view(V,:, t-2) .== 0.0] .= 3*ep.dt  # This sets the spike delays to 3 timesteps for the neurons who spiked 2 timesteps ago, emulating transmission delays or something
    end

end

function dv(v, sd, w, np, ep)
    k = sd .* exp.(-sd ./ np.τₛ) # This is just to save computations
    v.+ ((Eₗₜ .- v ./ np.τₘ ).- (v.-np.Eₑ) .*( w[2] * k) .- (v.-np.Eᵢ) .*( w[1] * k)) .* ep.dt  # This is the differential equation, evaluated with Euler
end

The function step! runs 10000 times, simulating 10 seconds of activity, and it takes ~350ms
I'd like to implement this in DiffEq, but I don't understand how to write a function in the way DiffEq wants it and having it computing the spikes.

Specifically I'm confused by:

  • How to keep track of the timestep inside the function
  • How I should define the matrix
  • What will solve do to my matrix: should I multiply by dt, or will solve do it?

I came up with this, I don't know if it makes any sense. I think there is a main problem in updating sd

# This function initializes all the needed arrays
function DEsimulate(tottime, np, sp, ep)
    alg = FunctionMap{true}()
    w = genweights(np, sp)
    v = zeros(np.N) .+ np.Vᵣ
    sd = zeros(np.N) .+ 0.2

    v[1:5] .= 0.

    p = (w, np, ep)
    prob = DiscreteProblem(update!, [v, sd], (ep.dt, tottime*ep.dt), p)
    sim = solve(prob, alg, dt=ep.dt)
    return sim

end

function update!(dv, u, p, t)
    w, np, ep = p

    v, sd = u
    v[v .== 0.0] .= np.Vᵣ
    v[v .> np.Vₜ] .= 0.0

    k = sd .* exp.(-sd ./ np.τₛ)
    dv[1] += ((Eₗₜ .- v ./ np.τₘ ).- (v.-np.Eₑ) .*( w[2] * k) .- (v.-np.Eᵢ) .*( w[1] * k))
    dv[2][v .== 0.0] .= 2*ep.dt
    dv[2] .+= 1
end

Any kind of hint, also on style or everything else is very well appreciated!

Stefano Bettani
@ginkobab
P.S. I don't care about error right now, I only want performance
Christopher Rackauckas
@ChrisRackauckas
@ginkobab Graham responded on the Slack but it looks like it didn't transfer over
Maybe you want to do something like this? https://tutorials.sciml.ai/html/advanced/01-beeler_reuter.html
BridgingBot
@GitterIRCbot
[slack] <oxinabox> I have rebooted it.
It should be back up shortly
Christopher Rackauckas
@ChrisRackauckas
great!
BridgingBot
@GitterIRCbot
[slack] <louisponet> Hi All, anyone else having an error when trying to do any solving of diffeq?
[slack] <louisponet> This happened at the solve step of the very first example
BridgingBot
@GitterIRCbot
[slack] <Donald Lee> Hi, is anyone familiar with what can cause this error?
LoadError: ArgumentError: invalid index: nothing of type Nothing
Full error in reply.
This message was deleted
[slack] <louisponet> probably you've tried to use the result of a findfirst or similar as the index into an array, but it returned nothing
BridgingBot
@GitterIRCbot
[slack] <Donald Lee> The error is coming from running solve . This line in the model function is in red:
du.GLC_c = vGLCc-1/p.rce*vGLCce-1/p.rcg*vGLCcg
[slack] <Donald Lee> vGLCc and so forth are algebraic equations written within the model function. Anything stand out as to why this error could've occurred?
[slack] <Donald Lee> I'm using LabelledArrays.jl , hence the du. and p. syntax.
BridgingBot
@GitterIRCbot
[slack] <louisponet> From looking at the code of that LabelledArrays.jl function, there is a findfirst that tries to find the symbol you are calling
[slack] <louisponet> could it be that you are trying to use a symbol that isn't actually in the LabelledArray?
[slack] <louisponet> that's the line I'm referring to
BridgingBot
@GitterIRCbot
[slack] <chrisrackauckas> @louisponet update your packages and get DataStructures v0.18
BridgingBot
@GitterIRCbot
[slack] <louisponet> Weird, I did that, normal up actually downgrades some packages back, e.g. DataStructures to v0.17. But then if I up each of the installed packages in the Project separately they all upgrade to the correct ones
[slack] <louisponet> That didn't work actually
BridgingBot
@GitterIRCbot
[slack] <chrisrackauckas> what do you mean?
BridgingBot
@GitterIRCbot
[slack] <louisponet> Okay, it was a sysimage issue
[slack] <louisponet> I think the system image I was using compiled in a lower version of DataStructures somewhere causing the error and also the weird updating behavior
[slack] <louisponet> sorry for the noise
Stefano Bettani
@ginkobab
@ChrisRackauckas Thanks for you answer, the tutorial looks very useful, I will look into that. How can I see Graham answer? I can't find any slack channel
BridgingBot
@GitterIRCbot
[slack] <chrisrackauckas> it's #diffeq-bridged on the slack
Stefano Bettani
@ginkobab
Coll thanks
Oh I'd need an invitation for that
Could you possibly copy paste his answer please?
BridgingBot
@GitterIRCbot
[slack] <chrisrackauckas> invitation is simple
[slack] <chrisrackauckas> http://slackinvite.julialang.org
[slack] <chrisrackauckas> but the message is

[slack] <chrisrackauckas> Graham Smith [1:19 PM]
ginkobab: your message got clipped going from gitter to slack, so I can't see your implementation starting around update!. But I've thought some about how I would implement a spiking network, so I'll try to answer your questions:

  1. The timestep is given to you through the argument t
  2. I'm not quite sure what matrix you mean, but I think you mean V, your membrane potentials? It's just the vector as long as np.N. You don't define the np.N x timesteps matrix; that comes out of solve.
  3. No need to multiply by dt (assuming I'm right about what you meant by the matrix); solve will take care of that. Eventually you may even want to use a more advanced solver, which would do way more than multiplying by dt
    Graham Smith [1:26 PM]
    None of that was unique to spiking networks, which I'm a little confused about. How is your original implementation tracking spikes?
    V[view(V,:, t) .> np.Vₜ, t+1] .= 0.0 # This makes the neurons over the threshold spike V[view(V,:, t) .== 0.0, t+1] .= np.Vᵣ # This reset the neurons that spiked to a low potential
    This block seems a bit off. Unless I'm missing something, it sets superthreshold potentials to zero, and then immediately to reset potential. What you really want is either to 1) mark in an auxiliary vector that there was a spike and then reset to some reset potential or 2) reverse these two lines and change 0.0 to some unattainable marker for "spike." That way V will have a marker for spiking timesteps, and you won't clobber it on the same step (as these lines do now, with 0.0 as the marker)
    [1:29 PM] Now the problem with all of these approaches is that they aren't differentiable. Which is really what I should have led with, but I was on a single track 😅

Graham Smith [2:00 PM]
Oooooo wait you can probably use callbacks to handle spike thresholding
[2:00 PM] https://diffeq.sciml.ai/v2.0/features/callback_functions.html

Chris Rackauckas [3:08 PM]
you probably want to link to recent docs. that's v2.0

Stefano Bettani
@ginkobab
Oh thanks!
BridgingBot
@GitterIRCbot

[slack] <ginkobab> Thanks for your answer!

Just to clarify, the weird block about updating sets the potential of the subsequent timestep equal to Vr or to 0, so the order is important, otherwise since 0 > threshold, the reset wouldn't work. So effectively it marks a spike that we can then extract!

I'm gonna look into callbacks now, thanks again!

[slack] <ginkobab> Really cool, that will work, and it lets me save only when spikes occur so I could save much memory and time
BridgingBot
@GitterIRCbot
[slack] <ashton.bradley> is there a new PR to watch?
[slack] <chrisrackauckas> I don't think so. @shashi what do you think the path is to get this in there? I know SymbolicUtils already has it, so it can't be so far off?
shrimpceviche
@shrimpceviche
In the Neural SDE setting, if we fit the data to the model, the model would ignore the noise, would go through the data exactly; the Brownian motion term goes to 0 (points made in the paper section 5). The paper used a latent model. How does DiffeqFlux solve this problem?
Jonathan Miller
@fieldofnodes
How do I git this channel on my slack?
Git is get, working on a Dvorak keyboard
Christopher Rackauckas
@ChrisRackauckas
@shrimpceviche look at the second tutorial in DiffEqFlux and you'll see how that's not the case
In fact, that argument doesn't even make sense. In many cases you need non zero noise to fit the data, otherwise you get trapped
6 replies
It's argued with examples or evidence, so I suggest you take a look at the examples and evidence which demonstrates that it doesn't occur, and it's clear from looking at the loss values why it can't occur.
Alex Wadell
@awadell1
Is there a mechanism to resume integration similar to odextend (https://www.mathworks.com/help/matlab/ref/odextend.html) in MATLAB? Specifically, I'm trying to switch callbacks after an event has occurred
Ghost
@ghost~5f97d833d73408ce4ff291dc

Hi all. Is there a way to deal with this problem in Julia?

function explicit(y,p,t)
sqrt(1-y[1]^2)
end
tspan = (0.0,π)
y0 = 0.0
problem = ODEProblem(explicit,y0,tspan)
sol = solve(problem, Rosenbrock23())

In MATLAB, Cleve Moler solve this problem by add a bound like this:
f = @(t,y) sqrt(1-min(y,1)^2).

This could also be used in Python with Scipy.odeint.
def f(t,y): return np.sqrt(1-np.min(y,1)**2)

But Julia don't allow this.