Hi Keith, First glance suggests that one place you should look is in the argument to while(). You're saying the while loop should continue so long as two conditons are met: that the midpoint of your function fx is not equal to the tolerance level you specified in the call to your function, and that i is less than the maximum number of iterations you presumably also specified elsewhere. Usually tolerance is the maximum difference between the output of subsequent iterations you will tolerate to be content with a solution. That is, if your first six iterations produce a sequence like .25, 1, .75, .79, .80, .80, ..., and if you set a tolerance of .01, you're saying that in this case you'll be content with the first five draws: .79 and .80 are sufficiently similar that something around .80 will be your solution. Hence, the point is not to run the algorithm until the midpoint of your function equals the tolerance level. The point is to run the algorithm until two subsequent estimates of a function's zero are within the tolerance level of eachother. Finally, check to be sure 'i' is defined: if all this takes place in a forloop iterating through different values of something you call 'i', you're fine. But the while loops do not automatically label each iteration 'i'. Hope this helps, Jenn On Wed, Feb 27, 2008 at 2:05 AM, Keith Schnakenberg <keith.schnakenberg at gmail.com> wrote: I've implemented the method of bisection using three embedded "while" loops. My problem is that, when I call for the function, it runs forever even though I have specified a maximum number of iterations. It has been running long enough that I suspect it is going to run it an infinite number of times. Without revealing my code for the whole problem, I'll show enough code demonstrate how I am telling it to stop after k iterations. while(fx(((x+y)/2)) != tol && i < iter.max){ i = i+1 while(){ while(){ } } } So, my first theory was that the other two loops were running infinitely (or a lot of times) within each iteration of the first while loop. However, I added "&& i < iter.max" to the end of the other while loops and this did not help. Other theories? _______________________________________________ gov2001-l mailing list gov2001-l at lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l _______________________________________________ gov2001-l mailing list gov2001-l at lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l