ode45 system of equations
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I used the lotkademo file as a template for solving a set of ODEs
When I change the initial conditions or time span the program still returns a solution vector from 0<t<15 (which was the default for the demo file) I've edited the function containing the equations as well and can't seem to see why these don't change. code below:
t0 = 0;
tfinal = 20;
y0 = [500 10]';
tfinal = tfinal*(1+eps);
[t,y] = ode45('MonodMod',[t0 tfinal],y0,[T Y]);
[T Y]
Given a function called MonodMod:
function yp = MonodMod(t,y)
yp = diag([- ((1*y(1))/(.5+y(1))) + 0 + 0,((1*y(1)*.8)/(.5+y(1))) - (0.7*.8) - (0.3*.8/1.42)])*y;
So when I update values for y0 or tfinal and evaluate [T Y] the ouput is still 0<t<15, and the initial values are still [20 20]..
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Risposte (2)
ME
il 12 Dic 2017
I have just been over this and found that
t0=0;
tfinal=20;
y0=[500 10]';
tfinal-tfinal*(1+eps);
[t,y]=ode45('MonodMod',[t0 tfinal],y0);
[t,y]
with the function
function yp = MonodMod(t,y)
yp = diag([- ((1*y(1))/(.5+y(1))) + 0 + 0,((1*y(1)*.8)/(.5+y(1))) - (0.7*.8) - (0.3*.8/1.42)])*y;
end
seems to work for me for a range of tfinal choices.
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Jan
il 12 Dic 2017
Modificato: Jan
il 12 Dic 2017
This is a very strange example. Using strings to provide the function to be integrated is outdated for 15 years now. Appending [T, Y] as parameter is deprecated for the same time also - see http://www.mathworks.com/matlabcentral/answers/1971.
[T,Y] is not defined or used anywhere. So what it is purpose? All you need and use is [t,y].
Perhaps this helps:
t0 = 0;
tfinal = 20;
y0 = [500 10]';
tfinal = tfinal*(1+eps); % Are you sure that this is useful?
[t,y] = ode45(@MonodMod, [t0 tfinal], y0);
function yp = MonodMod(t, y)
k = -0.72901408450704225; % -0.56 -(0.024 / 1.42)
yp = [-(y(1) / (0.5 + y(1)) * y(1); ...
(y(1)*0.8 / (0.5 + y(1)) + k) * y(2)];
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