Errors using fzero in rootfinding

ecc= 0.1
M= linspace(0, 2*pi, 800);

%%solving for psi using fzero
f = @(psi) psi- ecc*sin(psi)- M; 
psi = zeros(size(M));

for j = 1:length (M) 
    psi(j)=fzero(f,1);   
end

The original equaions is M = ψ - epsilon* sin ψ, trying to solve psi(M) for each M entry.

Could someone spot the errors in this? When I run the program, it show erros in fzero , "operands to the || and && operators ust be convertible to logical scalar values. Errors in fzero (line 307) else if ~ isfinite(fx) || ~isreal f(x)

Answer 1

[DGM]

Your problem is with how you set up your function. Your parameter M is a vector in the function definition, so at any given point, the function returns a vector. f(x) should return a scalar, not a vector. What your loop implies is that you're looking to find the root given M(j), so just do that.

ecc= 0.1
M= linspace(0, 2*pi, 800);
%%solving for psi using fzero
psi = zeros(size(M));
for j = 1:length (M) 
    f = @(psi) psi- ecc*sin(psi)- M(j); 
    psi(j)=fzero(f,1);   
end
psi