Fzero is not working

 isn=1.5;
h=5e-6;
x=2*pi*3e14;
%
fzero(@(y)(tan(sqrt(x.^2.*n^2/const('c')^2-y.^2)*h/2)-sqrt(y.^2-x.^2/const('c')^2./sqrt(x.^2*n^2/const('c')^2-y.^2))))

Fzero is unable to find the root

[JESUS DAVID ARIZA ROYETH]

what means const('c') for you?

[Walter Roberson]

And what is n ?

[dpb]

And

x=2*pi*3e14

? Really????!!!!

Dunno what Matlab actually does regarding argument reduction, but there's some real precision issues likely to arise there...

[Walter Roberson]

MATLAB does not do argument reduction for computations like that.

2*3e14 would be exactly representable as a double, by the way.

[dpb]

Yeah, but moving just a tad to find a solution...??? Altho as formulated, I guess it is just a constant so maybe it itself isn't a problem. What is range of y expected to be, I wonder, though?