How to solve an equation using numerical solver in Matlab?

aa
2020 9 30
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更新时间：2020 9 30
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Hi everyone,
I want to solve this equation using numerical solver. I have value of R and want to calculate the coressponding value of n using numerical solver.
May someone help me here ......
R =1/n^2 [(n+1)ln⁡(n+1)-n]

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Alan Stevens
Alan Stevens 2020-9-30

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Look up documentation on fzero.

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aa
aa 2020-9-30
I have no initial point to solve this ....
aa
aa 2020-9-30
>> x = fzero(@(x)x^(-2)*((x+1)*ln(x+1)-x)-0.44999)
Error using fzero (line 118)
The input should be either a structure with valid fields or at least two arguments to FZERO.
Alan Stevens
Alan Stevens 2020-9-30
Plot a curve of the right hand side Vs n, to see roughly where it equals R.
Alan Stevens
Alan Stevens 2020-9-30
You need to supply an initial guess. Also MATLAB use log not ln, for log to the base e.
Alan Stevens
Alan Stevens 2020-9-30
You need to pass the initial guess to fzero as its second argument.
aa
aa 2020-9-30
see i guess x=5 but still did not get the answer....
Alan Stevens
Alan Stevens 2020-9-30
Try
R = 0.44999;
f = @(n) ((n+1).*log(n+1)-n)./n.^2 - R;
n0 = 1; % Initial guess
n = fzero(f,n0);
disp(n)
aa
aa 2020-9-30
May you help me in generalizing this programme for large number of values. For example, I have more tahn 500 values of R and I want to calculate n for each values of R ....
John D'Errico
John D'Errico 2020-9-30
But what is wrong with writing a loop? Just wrap that code inside a loop, where you change R each time through.
aa
aa 2020-9-30
Earlier my code did not work with the loop but now I have fixed the error... it works perfectly .. Thanks

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