Solving a nonlinear equation using fsolve. cant reach at perfect result. output showing some error written below.

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pritha 2022-1-23

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评论： shiv gaur 2022-1-24

采纳的回答： Matt J

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Where M*_N = m - (a*sigma)

Equation solved. fsolve completed because the vector of function values is near zero as measured by the value of the

function tolerance, and the problem appears regular as measured by the gradient.

used code :

Result must be around 22-25. but itc coming .0029.

Is there anything wrong i am doing?

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Star Strider 2022-1-23

Since fsolve is a root-finding algorithm, plot the function to see if there are any zero-crossings. Since fsolve can find complex as well as real roots, it might be worth giving it complex initial parameter estimates to see what it finds.

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Matt J 2022-1-23

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编辑：Matt J 2022-1-23

在 MATLAB Online 中打开

Result must be around 22-25. but itc coming .0029.

As the plot shows, your function has no roots in the range 22-25

p = 1;

pfun=@(sigma) arrayfun( @(z)fun(z,p) , sigma);

fplot(pfun,[0,25])

xlabel sigma; ylabel fun

function sigmares = fun(sigma,p)

m = 939;

ms = 550;

b = -7.25*10^(-3);

gs = 8.238;

p0 = .15*(197.3)^3;

k = (1.5*p*p0*pi^2)^(1/3);

gss = (1 + (b*sigma/2))*gs;

m1 = (m-(gss*sigma));

F = ((1+(b*sigma))*gs*m1*(1/(2*ms^2*pi^3))*log((sqrt(k^2 + m1^2)+ k))) - sigma;

sigmares = F ;

end

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Walter Roberson 2022-1-24

It is the only real root. There might be several complex roots

shiv gaur 2022-1-24

use muller method

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