Busy- Message solving 1st order ODE

Hi Experts, I am new in Mathlab, and i have come across "busy" on the status bar when trying to solve simultaneous 1st order ODE. My questions are is mathlab taking time to compute or i have made an error on the code. Since i am a beginner, please simplify your response. Anyhelp is greatly appreciated. Thanks and below is the code: M-file

function dcdt= CELLULOSE(t,c)
%c(1)=c(A), c(2)=c(B), c(3)=c(C), c(4)=c(D), c(5)=c(E), c(6)=c(F), c(7)=c(G),
%c(8)=c(H), c(9)=c(I), c(10)=c(J), c(11)=c(K), c(12)=c(L), c(13)=c(M)
global K1 K2 K3 K4 TEMP R
dcdt=[-c(1)*(K1+K4); K1*c(1)-c(2)*(K2+K3); 0.95*K2*c(2); 0.25*K2*c(2); 0.20*K2*c(2);0.20*K2*c(2);0.25*K2*c(2); 0.20*K2*c(2);0.15*K2*c(2);0.1*K2*c(2);0.9*K2*c(2);0.65*K2*c(2);K3*c(2)];

Call Function:

>> clear all
>> global K1 K2 K3 K4 TEMP R
>> TEMP = 1000;
>> R=8.3141;
>> K1=(8*10^18)*exp(-46000/(R*TEMP));
>> K2=(1*10^9)*exp(-30000/(R*TEMP));
>> K3=(9.99*10^12)*exp(-10000/(R*TEMP));
>> K4=(8.10*10^7)*exp(-32000/(R*TEMP));
>> tspan =[0:400];
>> c0=[1 0 0 0 0 0 0 0 0 0 0 0 0]

c0 =

       1     0     0     0     0     0     0     0     0     0     0     0     0

>> [t,x]=ode45('CELL',tspan,c0);

Please help! please

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Jan]

Hi Dennis, I've formated your code for you this time.

[Dennis]

Hi Jan,

Where can i find the code?? Please help

[Walter Roberson]

Look on the left side of your posting. You will see an icon marked "Edit" there. If you click on that, you will be put in to an editor and can edit your question.

The link I posted before shows how to format your code nicely. It was http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Dennis]

Walter, Is that the code for my solution?? Did you find any erron on that code??

[Walter Roberson]

We do not have the original differential equations, so we are not going to be able to detect whether your code implements the correct equations or not.

You are asking that the equations be evaluated at a minimum of 401 points; the time for that is going to add up.

Using the Stats option like I discussed below should allow you to see some of the progress. And of course you could reduce your number of reference points in tspan to speed matters up.

Getting rid of global by parameterizing functions should contribute _some_ speed increase, but not necessarily a lot.

[Dennis]

Hi Walter, Is it possible that the problem that i stated takes more then few hours to solve??

[Walter Roberson]

It is possible. Why don't you try reducing tspan to 0:1 temporarily and see how long that takes to process.

If you want to see if you are getting somewhere, you could always display the parameters that were passed to CELLULOSE

[Dennis]

Walter, you are awesome man. It worked for tspan 0:1, that means my code is correct, i just need to wait. or may be get a faster computer. what you think??

[Walter Roberson]

Run something longer, say 0:10. Use tic before and toc afterwards to find out the elapsed time. You should be able to estimate the total required time from there.

Also, you have a lot of redundant operations. Recode CELLULOSE to have

K1c1 = K1*c(1);

K1c4 = K4*c(4);

K2c2 = K2*c(2);

K3c2 = K3*c(2);

dcdt=[-K1c1-K1c4; K1c1-K2c2-K3c2; 0.95*K2c2; 0.25*K2c2; 0.20*K2c2; 0.20*K2c2; 0.25*K2c2; 0.20*K2c2; 0.15*K2c2; 0.1*K2c2; 0.9*K2c2; 0.65*K2c2; K3c2 ];

Answer 1

[Walter Roberson]

It is recommended that you do not use "global". The alternative is http://www.mathworks.com/help/techdoc/math/bsgprpq-5.html

To get a better idea of what is going on in your routine, use odeset() to create an options structure that you pass to ode45. In particular you could ask for Stats http://www.mathworks.com/help/techdoc/ref/odeset.html#f92-1016858