Summing array entries 1

[JohnKGH]

Hey guys,

This is the opposite of my last question. How do you find sums of consecutive array entries? I need them to be displayed however and therefore cannot use the sume function. By this I mean [4 5 6 7] = [9 11 13]
Ultimately I want to use diff(x).*(sums of y).

 

[MikeyP]

A = [4 5 6 7];
answer = A(1:end-1) + A(2:end);

M

--
Dr Michael F Platten

 

[SomptingGuy]

It looks to me like you are doing numerical integration. If this is the case, take a look at Matlab's existng trapz() function.

 

[MikeyP]

I don't think so. trapz returns a single value and cumtrapz would not give the required answer.

M

--
Dr Michael F Platten

 

[SomptingGuy]

Let's wait and see. If the next question is: "Is there a way to sum all the elements of a vector and divide by two?" then I win!

 

[JohnKGH]

Guys I tried
for i = 1:1:length(array)-1
answer = x(i)+x(i+1)
end

Would this be a correct approach?

 

[JohnKGH]

*replace x with array*

 

[MikeyP]

No. For 2 reasons.

1) "answer" is being overwritten each time you go through the loop

2) You are using an unnecessary "for" loop

This is pretty basic stuff. I realise you are new to Matlab, but have you tried reading any books on the subject?

M

--
Dr Michael F Platten

 

[JohnKGH]

Yea Mike, im reading a MATLAB intro book for engineers. Unfortunately Im just beginning to program this week. BTW, your way definitely worked. So what you are saying is a for loop only gives one answer after many repetitions of mathematical calculation? Thanks

 

[IRstuff]

No, he's saying YOUR loop produces that result.

TTFN

 

[SomptingGuy]

JohnKGH,

Take a look at the sum() function. It looks purpose-built for your problem.

 

[dileeprd]

replace
answer = x(i)+x(i+1)

with
answer(i) = x(i)+x(i+1)

OR

answer = x(1:end-1)+ x(2:end)

which is the vector based approach as given by Mickey P