I think the idea there was to incrementally search for the roots. If you need a certain number of roots, you could use a WHILE loop that evaluates on the root counter. It often helps to know some details of the function in question. Can you post it?
Here is how I would modify the function.
function [z] = find_roots()
f = @(x) x.*cot(x)+99;
NR = 50; % The number of roots to find.
N = 150; % Fineness of the search, bigger is finer z = zeros(1,N);
rcnt = 1; % The root counter
cnt = 0; % The loop counter
while rcnt<=NR
cnt = cnt + 1;
for n = 1:N
try z(rcnt) = fzero(f,cnt+[(n-1)/N n/N]);
if abs(f(z(rcnt)))>1e-8
z(rcnt) = nan; % FZERO was messing with us
else
fprintf('Found a root at: %.5f\n',z(rcnt))
rcnt = rcnt + 1;
break % Put here only if root spacing is >1!
end
catch
end
end
end
x = 0:pi/50:max(z);
plot(x,f(x),'-',z,zeros(1,length(z)),'o')
line([0 max(z)],[0 0],'color','black')
axis([0 max(z) -1000.0 3000.0])
z = z(~isnan(z)); % Return only the needed values
