Error trying to solve 2 Second ODE
1 Ansicht (letzte 30 Tage)
Ältere Kommentare anzeigen
Hi,
I have a function that solves a differential equation using the RK method:
function [tvec, xvec] = rksolve(f, t0, tf, x0, dt)
%Solve f with initial conditions x0 between t0 -> tf
%with increments dt
%Set initial conditions
t = t0;
x = x0;
%Answer output
tvec = t;
xvec = x;
while t < tf
%RK method of solving
k1 = f(x, t);
k2 = f(x+0.5*k1*dt, t+0.5*dt);
k3 = f(x+0.5*k2*dt, t+0.5*dt);
k4 = f(x+k3*dt, t+dt);
x = x + ((k1 + 2*k2 + 2*k3 +k4)*dt)/6;
t = t+dt;
%Store outputs
tvec = [tvec t];
xvec = [xvec x];
end
But when I try to run it with the equations defined in func.m, it comes up with a horzcat error in the line:
xvec = [xvec x];
func.m:
function a = coords(x, t);
%Initial Conditions
xpos = x(1);
vx = x(2);
ypos = x(3);
vy = x(4);
a = [(-xpos - 2*xpos*ypos); (-ypos - (xpos^2) +ypos^2)];
%dxdt = vx
%dvxdt = -x -2*x*y;
%dydt = vy;
%dvydt = -y -(x^2) + y^2;
Any help would be greatly appreciated!
1 Kommentar
darova
am 15 Nov. 2019
What about preallocation?
n = round((tf-t0)/dt+1);
tvec1 = zeros(1,n);
i = 1;
while t < tvec
%% ...
tvec1(i) = t;
i = i + 1;
end
tvec = tvec1;
Antworten (1)
James Tursa
am 15 Nov. 2019
Bearbeitet: James Tursa
am 15 Nov. 2019
Just looking at func.m, it appears you pass in a 4-element x vector, but you only return a 2-element a vector. You need to return the derivative for all the states. So something like this instead based on your comments:
a = [ vx; (-xpos - 2*xpos*ypos); vy; (-ypos - (xpos^2) +ypos^2) ];
2 Kommentare
Siehe auch
Kategorien
Mehr zu Eigenvalue Problems finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!