Taking the sum of exponentials

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L'O.G. on 22 Mar 2022
Answered: Star Strider on 22 Mar 2022
To do the calculation,
is the following code correct? Is the (:) necessary? I think that makes a column vector, but I don't think it's necessary. I don't think cumsum would be useful here. Could somebody please advise? If it matters, . And a is a vector of .
x = linspace(0.01,100,10000);
f_x = sum(exp(-x./a(:)));
  1 Comment
Voss on 22 Mar 2022
Since a is already a column vector, the (:) is unnecessary, you're right.

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Accepted Answer

Star Strider
Star Strider on 22 Mar 2022
If it matters, . And a is a vector of .’
I don’t see ‘t’ defined anywhere, so it depends on what relationship ‘t’ has to ‘x’ or a.
However, since as @_ noted, since a is already a column vector by definition, the (:) is not necessary. The important aspect is that with respect to MATLAB coding, ‘x./a’ must be a matrix in order that sum produces the row vector necessary for the result.

More Answers (1)

Paul on 22 Mar 2022
Break it up with simple inputs to see what's going on:
x = [1 2]; % row vector
a = [1 2 3]; % row vector
x./a(:) % implicit expansion makes a 3 x 2 matrix
ans = 3×2
1.0000 2.0000 0.5000 1.0000 0.3333 0.6667
exp(x./a(:)) % element wise exp
ans = 3×2
2.7183 7.3891 1.6487 2.7183 1.3956 1.9477
sum(exp(x./a(:))) % sum down the columns
ans = 1×2
5.7626 12.0551





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