value search using functions

how do i use the fzero function or any other MATLAB function to find/verify the value of 'a', like i have done using the cubic spline method. (i am pretending that i don't know what that value is)

a=5;
w=-a:a/1000:a;
F=2*sin(a*w)./w; 
%
% 
w_int=-5:0.01:5;                              
F_int=spline(w,F,w_int);
plot(w_int,F_int,'o');
plot(w,F, '--', w_int,F_int,'o')
c = max(F_int); 
[~, idx] = min(abs(w_int - 0.005));
d = w_int(idx);
a1 = (c*d)/(2*sin(d));

Answer 1

[Walter Roberson]

You cannot do that. fzero() is based upon the assumption that when upper and lower bounds are provided, that they are constant, not values that vary according to the current "x" value. (Your "w" varies from -a to +a rather than being fixed.)