How to apply looping in iteration process ?

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Andi 2022-3-17

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评论： Mathieu NOE 2022-3-18

R_mean_value_0.01 .csv

在 MATLAB Online 中打开

Hi everyone,

I required to apply diffrent initail guess for iterative solutions. For a single solution, the following script works perfectly.

L = readmatrix('R_bounds_0.01.csv'); (coloumn matrix with 1986 rows)
for i=1:length(L);
f = @(n)((n+1)*log(n+1)-n)/n^2 - L(i);
n0 = 100; % Initial guess
n(i) = fzero(f,n0 );
disp(n );
end
nn=n';
csvwrite('N_lower_100.csv',nn);

However, i need to try with different values of initial guesses [0, 10, 100, 1000] etc. Someone suggets me a modified script but that is still not working,

A = readmatrix('R_mean_value_0.01.csv');
m = length(A) ; 
IG = [0, 10, 100, 1000] ;    % initial guess 
n = length(IG) ;
nn = zeros(m,n) ; 
for i = 1:n
    n0 = IG(i) ; 
    for j=1:m
        f = @(n)((n+1)*log(n+1)-n)/n^2 - A(j);    
        nn(i,j) = fzero(f,n0 );
        disp(nn(i,j) );
    end
end
csvwrite('N_mean_10000.csv',nn);

May someone suggest me any possibel solution.

Thank you!

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Torsten 2022-3-17

The implementation is correct.

I think the task of the assignment was to show you that the rootfinder may fail if the initial guess is far off. So there is nothing wrong with your code if fzero does not converge in all test cases.

Andi 2022-3-18

I agreed, sometime the initial guess is a bit far from the solution that why i used different initial guess. But that not works.

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回答（1 个）

Walter Roberson 2022-3-17

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https://ww2.mathworks.cn/matlabcentral/answers/1674039-how-to-apply-looping-in-iteration-process#answer_920609

在 MATLAB Online 中打开

If your initial guess is not between about -1 and about +40 then you might not get a solution.

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/930814/R_mean_value_0.01%20.csv';

A = readmatrix(filename);

syms N

f = @(n)((n+1)*log(n+1)-n)/n^2;

baseeqn = f(N);

fplot(baseeqn, [-1.5 40])

hold on

minA = min(A)

minA = 0.0706

maxA = max(A)

maxA = 0.9681

yline([minA, maxA]);

ylim([minA-1/4, maxA+1/4])

hold off

sol1 = vpasolve(baseeqn - A(1), 0.5)

sol1 =

15.859241089220361924912561179785

fplot(baseeqn, [32 40]); hold on;

yline([minA]);

hold off

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Andi 2022-3-18

If i run the same scipt using one initail guess, i can write the output in csv but when use for loop then i cant. This seems that tehre is no issue of directory.

Mathieu NOE 2022-3-18

在 MATLAB Online 中打开

N_mean_10000.csv

hello

a very minor bug in the first code posted is the initialization of nn is done with the wrong dimensions (flip m and n)

I have no problel running the corected code - attached the output file

of course the IG must contains only values strictly above -1 (otherwise log(n+1) is complex) and different from zero (division by zero)

A = readmatrix('R_mean_value_0.01.csv');
m = length(A) ; 
IG = [0.0001,0.001, 0.01, 0.1, 1, 10, 100, 1000] ;      % initial guess (n> - 1) and (n # 0)
n = length(IG) ;
nn = zeros(n,m) ; % mod here
for i = 1:n
    n0 = IG(i) ; 
    for j=1:m
        f = @(n)((n+1)*log(n+1)-n)/n^2 - A(j);    
        nn(i,j) = fzero(f,n0 );
        disp(nn(i,j) );
    end
end
csvwrite('N_mean_10000.csv',nn);