Re: [julia-users] ODE.jl - backwards (negative in time) integration
Nevermind, I realize that thought was silly because of how linear stability is defined. Carry on. Though I would still give a fixed timestep method a try to narrow down the bug to adaptive stepping. There may be some issue somewhere, something weird like how it chooses min/max timesteps? On Monday, June 27, 2016 at 6:15:45 AM UTC+1, Chris Rackauckas wrote: > > Won't some of the Runge-Kutta solvers be really unstable with a small > negative Delta t? What happens when you use a fixed time step method: does > it run and diverge? >
Re: [julia-users] ODE.jl - backwards (negative in time) integration
Won't some of the Runge-Kutta solvers be really unstable with a small
negative Delta t? What happens when you use a fixed time step method: does
it run and diverge?
On Friday, June 24, 2016 at 8:50:42 PM UTC+1, Mauro wrote:
>
> This is a bug, could you file an issue? Thanks! Note that some solvers,
> even some of the Runge-Kutta family work, for instance ode78, ode45_fe,
> ode21 or ode23s.
>
> On Fri, 2016-06-24 at 20:48, Chris <7hunde...@gmail.com >
> wrote:
> > 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
>
Re: [julia-users] ODE.jl - backwards (negative in time) integration
Submitted https://github.com/JuliaLang/ODE.jl/issues/104
Thanks.
On Friday, June 24, 2016 at 3:50:42 PM UTC-4, Mauro wrote:
>
> This is a bug, could you file an issue? Thanks! Note that some solvers,
> even some of the Runge-Kutta family work, for instance ode78, ode45_fe,
> ode21 or ode23s.
>
> On Fri, 2016-06-24 at 20:48, Chris <7hunde...@gmail.com >
> wrote:
> > 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
>
Re: [julia-users] ODE.jl - backwards (negative in time) integration
This is a bug, could you file an issue? Thanks! Note that some solvers,
even some of the Runge-Kutta family work, for instance ode78, ode45_fe,
ode21 or ode23s.
On Fri, 2016-06-24 at 20:48, Chris <7hunderstr...@gmail.com> wrote:
> 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
[julia-users] ODE.jl - backwards (negative in time) integration
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
