Serial summation within a for() loop

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Ali Dhukka
Ali Dhukka 2015-10-19
评论： Star Strider 2015-10-20
Summation Equations are a particular Achilles' Heel for me plus I'm a bit rusty on MATLAB these days. How I can algorithmize this equation?
where Δt_sup, q and t are each vector arrays. I was given this expansion as an example for Δt_sup(3):
Now I know that I need to do this within a for loop to iterate values for each corresponding value of Δt_sup(i), q(i) and t(i), but I'm not sure how to go about tackling this beyond the basic setup as such:
t_sup=zeros(length(q),1);
for i=1:length(q)
t_sup(i)= ???
end
Any help would be much appreciated.
  1 个评论
Stefan Raab
Stefan Raab 2015-10-19
You could use another for-loop within the for-loop which runs from 1 to i and adds the actual j-value in each step:
t_sup(i) = t_sup(i) + ((q(j) - q(j-1))/q(i))*log(t(i)-t(j-1)); % Caution: log10 for log to the base 10, log is for base e

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回答（1 个）

Star Strider
Star Strider 2015-10-19
You might not need any loops. See if this works:
q = randi(99, 10, 1); % Create Data (Column Vector)
t = [1:10]'; % Create Data (Column Vector)
dq = [diff(q); q(1)]/q(end); % ‘q-difference’ Vector
dt = [(t(end)-t(1:end-1)); t(end)]; % ‘t-difference’ Vector
Dt_sup = sum(dq .* log(dt)); % Δt_sup
  2 个评论
Ali Dhukka
Ali Dhukka 2015-10-20
Correct me if my understanding of what your script does is off, but I think I still need a for loop as I need to be able to find a value for Dt_sup at each time t and this script results with a scalar value for Dt_sup.
Star Strider
Star Strider 2015-10-20
My code calculates ‘Dt_sup’ for equal-length vectors of ‘t’ and ‘q’ defined in the code. My understanding of your code is that it is a scalar for given equal-length vectors of ‘t’ and ‘q’. It does not appear to be a function of ‘t’ otherwise. You can certainly loop through it with different vectors for ‘t’ and ‘q’, the only restriction being that the ‘t’ vector must be strictly monotonically increasing.
I just took the equation in your Question and coded it as presented. I have no idea what you’re doing, or the larger context of this equation.

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