# Adding a vector in a system of differential equations

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Aria Dae on 10 Mar 2020
Commented: James Tursa on 16 Mar 2020
I have a system of odes to be solved. The problem is that one of the odes contains iapp, which is a vector (same size as the time vector) i have from experimental data.
[time,output]=ode113('DiffEquations',time,init);
with:
function [output] = DiffEquations(time,init)
% defining variables and constants ...
% output(1,1)=....
% output(2,1)=(....
output(3,1)=(-iNa-iK+iapp)/C;
end
How should i input this vector in the function?

James Tursa on 10 Mar 2020
One way is to create a function handle to pass in the extra parameters. E.g.,
function [output] = DiffEquations(time,init,iapp) % <-- add iapp to the input argument list
[time,output]=ode113(@(t,y)DiffEquations(t,y,iapp),time,init); % <-- function handle with iapp

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James Tursa on 10 Mar 2020
This is telling you that your equation is wrong. If iapp is a vector, how can you possibly assign it to a scalar element of the derivative? You need to re-examine the equations you are simulating and compare it to the code you have written. Or post that for us to see so we can help you.
Aria Dae on 13 Mar 2020
Sorry for the confusion, i am not explaining myself well. Basilly, i have two vectors of data, the time vector and an Iapp vector (of the same size). What I am trying to compute is the voltage vector ( output(3,1) in the system of odes ) , which can be computed as such : dv/dt=(-iNa-iK+iapp)/C. The first two terms are expressed as functions of time which i wrote above. The iapp term, however, i have as a vector and i don't know how i can add the value of iapp at each second to the corresponding voltage at the same time.
Sorry again for the confusion, and thank you for the help!
James Tursa on 16 Mar 2020
If you don't know, then that means you don't understand your own set of odes. Is iapp perhaps a time sequence of values that you would need to interpolate? Again, we are guessing here until you can post the odes for us to look at.