fsolve stopped because of relative size of current step

I am trying to solve an equation using fsolve and I am getting the following error-

"fsolve stopped because the relative size of the current step is less than the

default value of the step size tolerance, but the vector of function values

is not near zero as measured by the default value of the function tolerance."

I am getting "No solution" even when I know that I should be getting a solution for all real values of psi. Can someone help me figure out what I need to change to get solutions.

syms y
psi = 0.1515;
r = 0.3;
a = r;
vf = [5 0];
m = 1;
x = linspace(-10*r,10*r);
x0 = ones(1,size(x,2));
opts = optimoptions(@fsolve,'Algorithm', 'levenberg-marquardt');
y = fsolve(@(y_val)solve_y(y_val,a,vf,x,psi,m),x0,opts);

% function solve_y
function F = solve_y(y_val,a,vf,x,psi,m)
    y = y_val;
    F = psi./norm(vf) - y - m*atan2(y,x+a) - m*atan2(y,x-a); 
end

[Alan Weiss]

I'm not at all sure that I understand what you are doing. Are you trying to solve for a bunch of scalar roots all at once, or is your objective really vector-valued? Why do you have a syms y call at the start of your script?

Alan Weiss

MATLAB mathematical toolbox documentation

[Sanjana Singh]

Yes, I forgot to eliminate the syms, thank you for pointing that out. I have a single equation in which I need to solve for y having all other values i.e psi, vf, a, m and a range of values for x. I wish to get a single y value corresponding to a each x value by solving the given equation (F = 0). Does this help?

Answer 1

[darova]

use for loop

syms y
psi = 0.1515;
r = 0.3;
a = r;
vf = [5 0];
m = 1;
x = linspace(-10*r,10*r);
x0 = ones(1,size(x,2));
F = @(y,x) psi./norm(vf) - y - m*atan2(y,x+a) - m*atan2(y,x-a); 
opts = optimoptions(@fsolve,'Algorithm', 'levenberg-marquardt');
for i = 1:length(x)    
    y0 = fsolve(@(y)F(y,x(i)),x(i));
    line(x(i),y,'markerk','*')
end