Output additional vectors from ode45

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Auwais Ahmed
Auwais Ahmed 2021-11-27
评论： Star Strider 2021-11-28
I am calculating concentrations and radii at all the timesteps within the ode45 loop. What is the best way to output all that information?

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Star Strider
Star Strider 2021-11-28
Ran in:
Adding additional outputs is permitted, providing that they are not used in the ode45 call. Normally, this is not a problem, because unless more outputs are requested in the calling script or function, only the first output is used.
The only way to recover them is to use the returned independent variable (usually time) vector and the solved dependent variables in a for loop and save the other desired output at each step of the loop.
tspan = [0 10];
ic = [0.1; -0.1];
[t,y] = ode45(@odefcn, tspan, ic);
for k = 1:numel(t)
[~,radii(k,:)] = odefcn(t(k),y(k,:));
end
figure
yyaxis left
plot(t,y)
ylabel('y(t)')
yyaxis right
plot(t, radii)
ylabel('Radius')
grid
function [dy,radius] = odefcn(t,y)
dy = zeros(2,1);
radius = hypot(y(1),y(2));
dy(1) = y(1);
dy(2) = radius * cos(y(1)) * sin(y(2));
end
.

更多回答（1 个）

Auwais Ahmed
Auwais Ahmed 2021-11-28
I am caluculating a value for a parameter eg radius at each time step in ode45. At the end I want to output all radius at all time t
  1 个评论
Auwais Ahmed
Auwais Ahmed 2021-11-28
In other words I just want to add an additional output argument in addition to the default y and t

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