calling exponential function to non linear square

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Zahra Safari 2020-9-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/592987-calling-exponential-function-to-non-linear-square

评论： Zahra Safari 2020-9-14

采纳的回答： Samiu Haque

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I want to fit data to an exponential function with the nonlinear least squares method, but MATLAB gives an error.

The code that I've written :

clear;
clc;
close all;
%mix code: ref_concrete_T8
tdata = ...
    [1.2560 2.7203 6.0830 10.0306 20.0960 40.9837 80.0923 ];
sdata = ...
    [1.3000 7.2567 23.0167 30.2733 31.9400 43.0667 43.4850 ];
            %fun=x1*exp(-(x2/tdata)^x3)
fun = @(x)x(1)*exp(-(x(2)./tdata)^x(3))-sdata;
x0=[40,0.9,0.1];
options = optimoptions(@lsqnonlin,'Algorithm','trust-region-reflective');
x = lsqnonlin(fun,x0)
plot(tdata,sdata,'ko')
hold on
tlist = linspace(tdata(1),tdata(end));
plot(tlist,x(1)*exp(-(x(2)./tdata)^x(3)),'b-')
xlabel time(day)
ylabel strength(MPa)
title('exponential Fit to Data ref conc T8')
legend('Data','exponential Fit')
hold off

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Samiu Haque 2020-9-13

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In your function you can't raise a matrix to a power. The only thing that is possible is to raise the power of each element in the matrix and for that the line should be

fun = @(x)x(1)*exp(-(x(2)./tdata).^x(3))-sdata;

Image Analyst 2020-9-13

Can you put this down in the answer section Samiu? You can even get credit for it down there. Thanks in advance.

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采纳的回答

Samiu Haque 2020-9-13

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/592987-calling-exponential-function-to-non-linear-square#answer_493954

在 MATLAB Online 中打开

In your function you can't raise a matrix to a power. The only thing that is possible is to raise the power of each element in the matrix and for that the line should be

fun = @(x)x(1)*exp(-(x(2)./tdata).^x(3))-sdata;

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Samiu Haque 2020-9-13

在 MATLAB Online 中打开

Use the following portion to solve the problem

syms tlist
y = x(1)*exp(-(x(2)./tlist).^x(3));
tlist = linspace(tdata(1),tdata(end));
y = subs(y);
plot(tlist,y,'b-')

Zahra Safari 2020-9-14

thank you.

how can i calculate the value of R-squared??

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