[julia-users] ODE.jl - backwards (negative in time) integration

[Chris]

Hello,

I came across this issue (recreated here using example code):

julia> using ODE

julia> function f(t, y)
           # Extract the components of the y vector
           (x, v) = y

           # Our system of differential equations
           x_prime = v
           v_prime = -x

           # Return the derivatives as a vector
           [x_prime; v_prime]
       end;

julia> # Initial condtions -- x(0) and x'(0)
       const start = [0.0; 0.1]
WARNING: redefining constant start
2-element Array{Float64,1}:
 0.0
 0.1

julia> # Time vector going from 0 to 2*PI in 0.01 increments
       time = 0.:-.1:-4pi;

julia> t, y = ode45(f, start, time);

This hangs for a long time (I've waited up to a minute before killing it). 
Is this a bug, or something I'm doing wrong? I do notice that reversing the 
time vector (-4pi:.1:0.0) yields a result.

Thanks,
Chris