# Help: numerical solution for first order differential (OD) equations

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Dushyant on 15 Sep 2013
I need some guidance regarding numerical ordinary differential equation
I have nine simultaneous first order differential (OD) equations which can be combinedly written as: dY/dt = A*Y + b where Y is a vector consisting of 9 terms and A is a matrix of size 9,3.
Can someone suggest me how should I start?
The paper that, I am looking at, briefly explains the procedure as: “The problem can be analytically without further simplification with the use of Matlab built-in function of matrix left division (\) and matrix power (expm 1) “ Regards, DK

#### 1 Comment

Azzi Abdelmalek on 15 Sep 2013
If Y is 9x1 array and A is 9x3 array, how can you do A*Y ?

Azzi Abdelmalek on 15 Sep 2013
A should be a 9x9 array
write and save this function as myeq.m
function dY=myeq(t,Y)
A=randi(9,9,9) ; % Example
b=1;
dY=zeros(9,1) ;
dY = A*Y + b;
Then call it
y0=zeros(9,1)% Initial conditions
tspan=[0 10];
[t,y]=ode45(@myeq2,tspan,y0)

#### 1 Comment

Azzi Abdelmalek on 16 Sep 2013
[ Dushyant commented]
Thanks.
Sorry, I mistakenly wrote wrong dimension for A.
Regards, Dushyant