working on a bisection code and im pretty lost is it right so far?

function [xr ea iter] = bisect(func,x1, xu, es, maxit)
if func(x1)*func(xu)>=0, error('no sign change'); end
xold = x1;
for iter=1:maxit
  xr = ???
  test = func(x1)*func(xr)
  ea = abs((xr-xold)/xr)*100;
  if test<0, xu = xr;
  elseif test>0;  ???;
  else ea = 0;
  end

[John D'Errico]

Please use the code formatting button "{} Code" when you post code. Your code is unreadable as it is.

[John D'Errico]

Having fixed your code (I'll do that once) to make it readable...

Is it right? Of course not.

You have assignments like

xr = ???

and

???;

That last was a good one, though not truly valid syntax. I'll admit that when I stop writing code to take a rest, I usually add a random line like

jw56ywykmej

This way I cannot miss finding it when I resume work later on. At the very least, mlint will tell me about it.

Your code is missing end statements. Lots of other issues I could pick at. For example, why use a for loop instead of a while loop? A for loop forces the code to run for maxit iterations. What if it has converged before then? Yes, this last is a minor issue that relates to efficiency, instead of does the code work.

Essentially, you are going in a reasonable direction, but you are not there yet. So why not finish writing it? Try it out? Learn to debug your code, so learn to use the debugger.