You cannot use fminbnd to guarantee a distance of 0.01 (or any other distance) to the global minimum, but typically you will do much better than that with the default tolerances. To eliminate your fminbnd error message remove the line, r=q:0.01:w,
e=fminbnd(@fun,q,w)
function [c]=fun(r)
%r=q:0.01:w;
l=(1000./r)-(0.25*pi.*r);
c=(50*pi.*r)+(((2.*r)+(2.*l))*40);
end
You can however guarantee a distance of 0.01 if you use exhaustive search, instead of fminbnd. That would look like,
r=q:0.01:w;
[~,minloc]=min(fun(r));
e=r(minloc)
function [c]=fun(r)
l=(1000./r)-(0.25*pi.*r);
c=(50*pi.*r)+(((2.*r)+(2.*l))*40);
end
