How to terminate ODE at particular point?

I have defined this ODE as function qd2=odefcn2(t2,q2)

where t2=pi/4:0.5:pi/2; and q2=[ [q12;q22;q32];

after running above ODE I am getting result as

4.1706 9.2403 1.5708

4.2743 9.3530 1.5707

4.3779 9.4658 1.5705

4.4816 9.5785 1.5704

4.5853 9.6912 1.5703

4.6889 9.8040 1.5701

4.7926 9.9167 1.5700

4.8963 10.0294 1.5699

4.9999 10.1422 1.5697

5.1036 10.2549 1.5696

5.2073 10.3676 1.5695

5.3109 10.4804 1.5693

5.4146 10.5931 1.5692

5.5183 10.7058 1.5691

5.6219 10.8186 1.5690

5.7256 10.9313 1.5688

5.8293 11.0440 1.5687

5.9329 11.1568 1.5686

6.0366 11.2695 1.5684

6.1402 11.3822 1.5683

6.2439 11.4950 1.5682

6.3476 11.6077 1.5680

6.4512 11.7204 1.5679

6.5549 11.8332 1.5678

6.6586 11.9459 1.5676

6.7622 12.0586 1.5675

6.8659 12.1714 1.5674

6.9696 12.2841 1.5672

7.0732 12.3969 1.5671

7.1769 12.5096 1.5670

7.2806 12.6223 1.5668

7.3842 12.7351 1.5667

7.4879 12.8478 1.5666

7.5916 12.9605 1.5664

7.6952 13.0733 1.5663

7.7989 13.1860 1.5662

7.9026 13.2987 1.5660

8.0062 13.4115 1.5659

8.1099 13.5242 1.5658

8.2136 13.6369 1.5657

8.3172 13.7497 1.56

these are total 41 rows ,if i want to stop at q(30,:) what is the matlab code for this?

thank you

Answer 1

[Ameer Hamza]

If you just want to delete the solutions after forty lines of code, then you can do it like this

q(31:end, :) = []

However, if you want to stop the ode solver at that point, then read about ODE events: https://www.mathworks.com/help/matlab/ref/odeset.html#d122e899781. Also check the example here: https://www.mathworks.com/help/matlab/math/ode-event-location.html

[sangita kamat]

Thank you very much for your prompt response. Shall try your suggestion.

[sangita kamat]

after using above cod provided by you, im getting msg "Subscripted assignment dimension mismatch."

Can you explain me why im getting this message?

thank you

[Ameer Hamza]

After this line???

q(31:end, :) = []

Can you show output of

size(q)

Or can you show the code which solves the ODEs.

[Walter Roberson]

If q was smaller than 31 rows, then 31:end would be 31 to something less than 31, which would be the empty vector, and that is valid indexing -- that is, there would be no error and no rows would be removed.

So it would have to be something else causing the problem.

[sangita kamat]

size(q2)= 41 3

still i am not getting it

[Ameer Hamza]

Can you share the code?

[sangita kamat]

My this ODE is one of the ODEs , part of one main file. What code do you want?

My ODE code is

function qd2=odefcn2(t2,q2)

k21=5; xT=44,yT=32

k22=0.01;fr2=5;fa2=0.02;

t2 =pi/4:0.5:pi/2;

[Ameer Hamza]

How is odefcn2 defined? This code does not assign any value to qd2. Also, how are you calling ode45?

[sangita kamat]

sorry not under ODE45 ,under function

function qd2=odefcn2(t2,q2)
  qd2=[ dxdt ; dydt ; dtheta dt];
q2=[q12;q22;q32];
q20=[  4.1706    9.2403    1.5708];
dxdt=ucos(theta)
dydt=usin(theta)
d(theta)dt=  v

where u= some value , v= some value

[sangita kamat]

thank you very much ,above code to stop ode is working .

 t2  =pi/2:0.5:3*pi/4; 
[t2,q2]=ode45(@odefcn2,t2,q20)