Track variables within DifferentialEquations.jl function

@erlebach wrote:

Hi,

I have a simple function to solve:

using DifferejntialEquations, Plots, BenchmarkTools

var = []
function coupledd!(du, u, p, t)
    α, β, D1, D2 = p
    c1, c2 = u
    dc1  = α*c1 + D1 * (c2-c1)
    dc2 = β*c2  + D2 * (c1-c2)
    push!(var, c2)
    du .= [dc1, dc2]  # note the broadcast operator!
end

u0 = rand(2)
tspan = (0.,10.)
pars = [-.2, -.1, 1., 1.]
prob = ODEProblem(coupledd!, u0, tspan, pars)
sol = solve(prob, Tsit5())
println("size(var)= ", size(var))
println("nb time steps= ", size(sol.t))

size(var) returns 696
size(sol.t) return 12

However, when I print var, I get the output:
87-element Array{Any,1}

which seems to imply that Tsit5() calls the right-hand side 8 times every time step.

What I am interested in is the value of a variable at every time step (once per time step). So I would like to monitor variables. Is there a facility for that? Thanks.

Gordon

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