How to "keep" a variable for some rows within a for loop

Hi,

My problem is the following:

I've created a for-loop in which I calculate SOMETHING(i) for each row (see code below). But I'm not able to keep the variable "SOMETHING" for some rows since i updates this variable in each row.

My goal is not to use the current variable SOMETHING of (i) in each row, I rather wanna calculate c with the same "SOMETHING" for 10 rows.

For example:

In the first 10 rows I would like to use SOMETHING(1) for my calculation of variable c and in row 11 I would like to use

SOMETHING(11) = SOMETHING(1) + c(1) + c(2) + c(3) + c(4) + c(5) + c(6) + c(7) +c(8) + c(9) + c(10)

With SOMETHING(11) I would like to calculate c for the next 10 rows again and so on...

Is there a way to achieve this?

Would I need to use another for loop?

MANY THANKS!!!

WRONG CODE:

for i = length(a)
    c(i) = a(i) + b(i) * SOMEHING(i)
    SOMETHING(i) = c(i) + SOMETHING(i) 
end                                                                                           

Answer 1

[Ameer Hamza]

Try something like this

for i = 1:length(a)
    idx = floor((i-1)/10)*10 + 1;
    c(i) = a(i) + b(i) * SOMEHING(idx);
    if mod(i,10)==1
        SOMETHING(idx) = c(idx-9:idx) + SOMETHING(idx);
    end
end

[buhmatlab]

This approach seems really promising but I'm still confused:

Consider we are in row 10 (i = 10) then idx would be equal to idx = 11.

As c needs to be calculated, I would use SOMETHING(11) which is not calculated in row 10?

[Ameer Hamza]

I missed that point. Check the updated answer.

[buhmatlab]

Thank you so much for your help but the only change I've noticed is that you replaced 10 by 9 within the if-clause. Since this is only relevant when i = 11 it does not solve my problem. If i would be equal to 10 then idx would be 11.

But c(10) could not be calculated since it would use SOMETHING(11) which is not existent at this step or am I wrong?

[Ameer Hamza]

No, I chaged this line

idx = floor((i-1)/10)*10 + 1;

Now

i = 10 => idx = 1;
i = 11 => idx = 11;

[buhmatlab]

Sorry, my bad! Now it makes (almost) sense to me, BUT:

Even if i = 11 and idx = 11, c cannot be calculated since SOMETHING(11) is not existent (the if clause is "not used" before).

I would need a calculation for SOMETHING in the last row before the "switch" happens (e.g. row 10) so that the latest value (SOMETHING(1)+c(1:10)) is filled in SOMETHING(11).

[Ameer Hamza]

Why not move it in this order?

for i = 1:length(a)
    idx = floor((i-1)/10)*10 + 1;
    if mod(i,10)==1
        SOMETHING(idx) = c(idx-9:idx) + SOMETHING(idx);
    end
    c(i) = a(i) + b(i) * SOMEHING(idx);
end

[buhmatlab]

Oops! Unfortunately I was out of my mind...this little tweak makes totally sense!

Thank you so much!!!

[Ameer Hamza]

I am glad to be of help.