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Calculating the difference between a vector and time

Asked by Nikolaos Zafirakis on 4 May 2019
Latest activity Commented on by Star Strider
on 5 May 2019
I'm looking for a way to get this loop to work, basically I need to calculate the difference in a 3x1 vector divide by the difference in time. Does anyone have any suggestion?
t = 2000
n= 0;
for ind = 0:1:t
n= n+ind;
S(n) = (diff(x( don't know how to input the value here )))./diff(t(ind)); %x is a three element vector
end

  5 Comments

dxdt = diff(x)./diff(t);
So, the diff command wont work for this because if
A = [1 1 2 3]
diff(A)
= [ 0 1 1 2]
where I would need the ouput to be
=[1 0 1 1]
because
Delta_A(1) = 1 - 0 = 1 % first element - no element
Delta_A(2) = 1 - 1 = 0 % second element - first element
Delta_A(3) = 2 - 1 = 1 % third element - second element
Delta_A(4) = 3 - 2 = 1 % four element - third element
If you are ‘padding’ ‘A’ with an initial 0, you need to tell MATLAB.
MATLAB does many things well, although it is sadly deficient when it comes to mind-reading.
Try this:
A = [1 1 2 3];
dA = diff([0 A])
producing:
dA =
1 0 1 1
NOTE — You need to do similar ‘padding’ for your time vector.

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1 Answer

Answer by Omer N
on 5 May 2019

Try this:
A = [1 1 2 3];
A-[0,A(1:end-1)]
ans =
1 0 1 1

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