How is f(x) evaluated for each iteration using fsolve?

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I'm using fsolve for an unconstrained non-linear function. And I notice that fval is much different than f(x) for the last iteration. How exactly is f(x) calculated?
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Stephen23
Stephen23 on 14 Jan 2019
Edited: Stephen23 on 14 Jan 2019
"I got confused because it says f(x) even though it's the sum of squared function values."
I agree that the inconsistent labeling is confusing at best, and at worst incorrect. You should make a bug report (and include a link to this thread).

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Accepted Answer

Martijn
Martijn on 15 Jan 2019
The values shown under f(x) in the iteration table are indeed not literally the function values at that given iteration, you are seeing the square of the norm of the function value vector here; as documented, see:
The reason for this is that "fsolve" can actually solve whole systems of equations where f(x) would then be a whole vector of values. Displaying this whole vector in the table is not really feasible, there is not enough space for that. Hence, instead, a measure is shown which basically summarizes the whole f(x) vector in a single measure which also actually is representative for how good the current solution is.
We could look into whether we can perhaps change the header to ||f(x)||^2 in future releases to better illustrate this.

More Answers (1)

RANJEET YADAV
RANJEET YADAV on 14 Jan 2019
f(x)=fsolve(@(x) funname(x),x=1);

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