How to evaluate parameters in sum() of handle functions with fminsearch

4 次查看（过去 30 天）
3Nz0
3Nz0 2021-10-24
评论： 3Nz0 2021-10-24
I have some problems with the evaluation of parameters in a sum of handle functions
x_exp and y_exp are known vectors.
I want to evaluate the parameters in the following function:
The idea is to use fminsearch to evaluate g(i) and t(i): ObjFunc=@(g,t)sum((y_exp-y_eq(x))^2/(y_exp^2))
Looking in the community, I tried to use:
x_exp=rand(1,10); %just to define the known vectors
y_exp=rand(1,10);
n=3;
g=rand(1,n);
t=rand(1,n);
syms x i
y_eq = matlabFunction( symsum(g.*exp(-x_eq./t), i, 1, n));
My question is: "How can I evaluate g(i) and t(i)?
Thank you in advance
  2 个评论
John D'Errico
John D'Errico 2021-10-24
编辑：John D'Errico 2021-10-24
This is a question I see often, where somene feels they need to introduce symbolic parameters. When there is no reason to use a symbolic expression, DON'T! That you don't know the value of something does not mean it must be symbolic. And, as soon as you make things symbolic, you make MATLAB run MUCH more slowly.
As you can see in the answer you got, no symbolic parameters needed to be created or involved.
3Nz0
3Nz0 2021-10-24
Sorry, I know it is not necessary to use the symbolic parameters.
I solved the problem but, actually, I really don't know how to make this in an automatic way.
My mfile (posted in the other comment) works fine, but an adaptive mfile depending on "n" should be great.
Thank you.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Sargondjani
Sargondjani 2021-10-24
Take a look at this. I hope it helps.
x_exp=rand(1,10); %just to define the known vectors
y_exp=rand(1,10);
n=3;
g=rand(1,n);
t=rand(1,n);
%Create function handle:
fun_eq = @(g,t,x_eq)sum(g*-exp(-x_eq/t));
% Evalute y_eq for g(2) and t(2):
ii = 2;
y_eq = fun_eq(g(ii),t(ii),x_exp);
% Use fminsearch as follows:
%Define the objective
ObjFunc = @(g,t,x_,y_)sum((y_-fun_eq(g,t,x_)).^2./(y_.^2));
% Use x_exp and y_exp as input x_ and y_, and g and t are inputs x(1) and (x2)
[sol] = fminsearch(@(x)ObjFunc(x(1),x(2),x_exp,y_exp),[1,1])
  5 个评论
显示 3更早的评论
Sargondjani
Sargondjani 2021-10-24
编辑：Sargondjani 2021-10-24
There is one thing. I think the argument in fminsearch needs to be a vector. So you would need a transformation. So:
ObjFunc=@(B) sum(((y_exp-fun_y_sum(x_exp,B(1:n),B(n+1:2*n))).^2)./y_exp.^2);
B0=rand(2*n,1);
[B_est, SSE] = fminsearch(ObjFunc, B0)
B_est = [B_est(1:n),B(n+1:2*n)]
with
function y_sum = fun_y_sum(x,B1,B2)
y_sum = 0;
for ii = 1:size(B1,1)
y_sum = y_sum + B1(ii,1)*exp(-x/B2(ii,1));
end
end
3Nz0
3Nz0 2021-10-24
I don't know, in the old script B was a matrix in fminsearch().
Again, many thanks for your help

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Surface and Mesh Plots 的更多信息

标签

产品


版本

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by