MATLAB: How get the maximal positive root of polynomial

Question

I have such a function which computes positive roots of 8th order polynomial.

 function res = lambdazero1( l, a )
p = [-2 * l^4, 0, l^4 * (3 * a^2 - 2 * l^2 + 3), 0, 0, 0, l^2 * ( l^2 -3 * a^2 + a^6 * ( l^2-3 ) ), 0, 2 * a^6];
sol = roots(p);
res = sol(imag(sol) == 0 & sol > 0);
end

It turns out that for some values of "l" and "a" it has several positive roots. Any idea how to get the maximal positive root?

Many thanks in advance.

Answer 1

Add

res = max(res)

in your code from above.

Best wishes

Torsten.