Can someone help me with my code? Topic: integration

Hi everyone!

I am going to calculate the integral of a function V(j). I have already found the values for V and j. I am going to use the following formulas to calculate the integral:

S(j) = S(j-1) + 1/2V(j-1)+1/2V(j) for j>=1

S(0) = 0 for j= 0

How can I write this in matlab? Hope someone can help me out here :)

[KSSV]

YOu want to put that into loop?

[LB]

Yes! And I don't know exactly how to write it to get the correct values.

Answer 1

[Andrei Bobrov]

out = trapz(V);

or

out = sum(V) - sum(V([1,end]))/2;

or

S = cumtrapz(V);

or

S = [0,cumsum(sum([V(1:end-1);V(2:end)])/2)];

or

S = [0;cumsum(filter2([.5;.5],V(:),'valid'))];

Answer 2

[Luca Fenzi]

Dear LeneB, You should truncate the sum (S(j) = S(j-1) + 1/2V(j-1)+1/2V(j) for j>=1) up to N: in this way knowing V(j) for all j you can evaluate S with the following code:

N=10000; %%Truncation order of the sum
S=zeros(1,N); % Initialisation of the vector S
             % S(1)=0 corresponds to S(0)=0 for j=0
% Define V(j) for j=1:N.
for i=2:N
  S(i) = S(i-1) + 1/(2*V(i-1))+1/(2*V(i))
end