# Use with GPUs

Note that the differential equation solvers will run on the GPU if the initial condition is a GPU array. Thus, for example, we can define a neural ODE by hand that runs on the GPU (if no GPU is available, the calculation defaults back to the CPU):

using DifferentialEquations, Flux, Optim, DiffEqFlux, DiffEqSensitivity

model_gpu = Chain(Dense(2, 50, tanh), Dense(50, 2)) |> gpu
p, re = Flux.destructure(model_gpu)
dudt!(u, p, t) = re(p)(u)

# Simulation interval and intermediary points
tspan = (0.0, 10.0)
tsteps = 0.0:0.1:10.0

u0 = Float32[2.0; 0.0] |> gpu
prob_gpu = ODEProblem(dudt!, u0, tspan, p)

# Runs on a GPU
sol_gpu = solve(prob_gpu, Tsit5(), saveat = tsteps)

Or we could directly use the neural ODE layer function, like:

prob_neuralode_gpu = NeuralODE(gpu(dudt2), tspan, Tsit5(), saveat = tsteps)

If one is using FastChain, then the computation takes place on the GPU with f(x,p) if x and p are on the GPU. This commonly looks like:

dudt2 = FastChain((x,p) -> x.^3,
FastDense(2,50,tanh),
FastDense(50,2))

u0 = Float32[2.; 0.] |> gpu
p = initial_params(dudt2) |> gpu

dudt2_(u, p, t) = dudt2(u,p)

# Simulation interval and intermediary points
tspan = (0.0, 10.0)
tsteps = 0.0:0.1:10.0

prob_gpu = ODEProblem(dudt2_, u0, tspan, p)

# Runs on a GPU
sol_gpu = solve(prob_gpu, Tsit5(), saveat = tsteps)

or via the NeuralODE struct:

prob_neuralode_gpu = NeuralODE(dudt2, tspan, Tsit5(), saveat = tsteps)
prob_neuralode_gpu(u0,p)

## Neural ODE Example

Here is the full neural ODE example. Note that we use the gpu function so that the same code works on CPUs and GPUs, dependent on using CUDA.

using DiffEqFlux, OrdinaryDiffEq, Flux, Optim, Plots, CUDA, DiffEqSensitivity
CUDA.allowscalar(false) # Makes sure no slow operations are occuring

# Generate Data
u0 = Float32[2.0; 0.0]
datasize = 30
tspan = (0.0f0, 1.5f0)
tsteps = range(tspan, tspan, length = datasize)
function trueODEfunc(du, u, p, t)
true_A = [-0.1 2.0; -2.0 -0.1]
du .= ((u.^3)'true_A)'
end
prob_trueode = ODEProblem(trueODEfunc, u0, tspan)
# Make the data into a GPU-based array if the user has a GPU
ode_data = gpu(solve(prob_trueode, Tsit5(), saveat = tsteps))

dudt2 = FastChain((x, p) -> x.^3,
FastDense(2, 50, tanh),
FastDense(50, 2))
u0 = Float32[2.0; 0.0] |> gpu
p = initial_params(dudt2) |> gpu
prob_neuralode = NeuralODE(dudt2, tspan, Tsit5(), saveat = tsteps)

function predict_neuralode(p)
gpu(prob_neuralode(u0,p))
end
function loss_neuralode(p)
pred = predict_neuralode(p)
loss = sum(abs2, ode_data .- pred)
return loss, pred
end
# Callback function to observe training
list_plots = []
iter = 0
callback = function (p, l, pred; doplot = false)
global list_plots, iter
if iter == 0
list_plots = []
end
iter += 1
display(l)
# plot current prediction against data
plt = scatter(tsteps, Array(ode_data[1,:]), label = "data")
scatter!(plt, tsteps, Array(pred[1,:]), label = "prediction")
push!(list_plots, plt)
if doplot
display(plot(plt))
end
return false
end
result_neuralode = DiffEqFlux.sciml_train(loss_neuralode, p,
maxiters = 300)