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

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pritha on 23 Jan 2022
Commented: shiv gaur on 24 Jan 2022
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?
  1 Comment
Star Strider
Star Strider on 23 Jan 2022
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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Accepted Answer

Matt J
Matt J on 23 Jan 2022
Edited: Matt J on 23 Jan 2022
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);
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 ;

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