How to use ODE45 with multiple initial conditions?

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Blake
Blake 2015-10-5
回答： Torsten 2015-10-6
I"ve created a function that uses ode45 to draw solution curves for an equation in the x1x2-plane this phase portrait is supposed to be on the same plot as a direction field as well as plot the initial conditions. My coding for the phase portrait is as follows:
function [ output_args ] = phasePortrait(A,tmin,tmax,x1init,x2init)
%UNTITLED3 Summary of this function goes here
% Detailed explanation goes here
directionField(A)
hold on
f= @(t,y) [A(1,1).*y(1) + A(1,2).*y(2);A(2,1).*y(1) + A(2,2).*y(2)];
[t,y]=ode45(f,[tmin, tmax],[x1init, x2init]);
hold on
plot(y(:,1),y(:,2))
hold on
plot(x1init, x2init)
axis(-2.5,2.5,-2.5,2.5)
title('Phase Portrait')
xlabel('x1(t)')
ylabel('x2(t)')
end
*When I call the function I get an error saying that I have vectors of different lengths for the intial conditions and the results. How do I fix this or am I imputing something wrong?*
tmin=0
tmax=20
A=[-1 2;-2 -1]
x1init=[-2.5 1.5 2.5 -2.5]
x2init=[0 -2.5 0 2]
figure
phasePortrait(A,tmin, tmax, x1init, x2init)

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回答（1 个）

Torsten
Torsten 2015-10-6
Call ode45 four times in a loop, first for [x1init(1) x2init(1)] as initial condition, then for [x1init(2) x2init(2)] as initial condition and so on.
Best wishes
Torsten.

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