fsolve within fsolve -> update initial guess

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Tintin Milou
Tintin Milou 2022-5-15
评论： Matt J 2022-5-15
Hello,
I am using fsolve within fsolve. That is, for each iteration of the outer fsolve loop, matlab solves the inner fsolve problem.
Is there a possibility to use the previous guess for the inner fsolve problem. I tried the following
function F = solvep(p,x0,par)
% some calculations
x = fsolve(@(x) solvex(x,par2),x0);
x0 = x;
% some more calculations
F = p*x - 1;
end
But for some reason, matlab does not update x0. That is, x0 is always set to x0 as given in the first line. I hope to speed up the procedure a bit by using the previous guess because most of the time, the changes in p that matlab considers are quite minor.
Thanks!
  1 个评论
Matt J
Matt J 2022-5-15
In your code, the sub-problem and its solution x does not appear to depend on p. Therefore, you should probably just pre-compute it.

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采纳的回答

Matt J
Matt J 2022-5-15
function F = solvep(p,x0,par)
persistent X0
if isempty(X0), X0=x0; end
% some calculations
x = fsolve(@(x) solvex(x,par),X0);
X0 = x;
% some more calculations
F = p*x - 1;
end

更多回答（1 个）

Walter Roberson
Walter Roberson 2022-5-15
Have solvep() return x0 as well, and update the appropriate variable in the calling function.
Or you could back-calculate what x would have to be in order to produce the given F.
Both possibilities imply using a real function for the outer layer instead of an anonymous function. Values bound into an anonymous function cannot be changed by using techniques such as assignin()

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