saveat begin time

[ArnoStrouwen]

Should it work like this?

using OrdinaryDiffEq
f(u,p,t) = 1.01*u
u0 = 1/2
tspan = (0.0,1.0)
prob = ODEProblem(f,u0,tspan)
sol = solve(prob, Tsit5(), saveat=[0.0,0.0,0.5,0.5,1.0,1.0])
println(sol.t)
[0.0, 0.5, 0.5, 1.0, 1.0] # why no dubbel 0.0 like the others?

[ChrisRackauckas]

I wouldn't say the doubling behavior is really intentional, I just don't think we've looked at this non-unique case too closely. We can make it double, though I really wonder what the use is here.

[ArnoStrouwen]

Measurement time optimization is the use case. Though in 99.9% of cases it is much to just save a dense solution and then interpolate it at the desired times, instead of working with saveat keyword. It came up for me once when I was doing joint initial condition and measurement time optimization and could not save the dense solution because I ran out of memory. Took me some time to figure out why my objective was discontinuous when multiple measurements got put to t0. Still, it is not difficult to check for uniqueness myself.

[ChrisRackauckas-Claude]

Triage: This is an edge case with duplicate values in saveat. Chris noted the doubling behavior is not intentional, and the use case (measurement time optimization) is better served by dense output interpolation. Minimal impact. Recommend closing.