Why MATLAB gives me this warning?

Check function or try again with a different starting value. Exiting fzero: aborting search for an interval containing a sign change because NaN or Inf function value encountered during search. (Function value at 2.96273e+152 is -Inf.)

MATLAB gives me this warning on command window, but it still does calculations corretly after this warning. Is this an error? I have seen this warning for first time.

Thanks

[Volkan Yangin]

OK, i obtained the problem. First value of the function runs with 0 starting value and it gives me the warning.

Answer 1

[Rik]

You are trying to find a zero of a function. This means Matlab will look for an x-value where the sign changes. During this proces it encountered a -inf value, after which it broke off its search.

What you need to do is written in the warning message: either check if your function is indeed the function you ment (i.e. check for typos), or adjust the starting value. If you have the function y=x and you start looking a x=100 and only increasing x, you'll never find the crossing. Apparently something equivalent has happened here.

Your Matlab is not broken, it just did not find the result it was looking for.

[Volkan Yangin]

Thank you Rik Wisselink .

[Ryland]

Is there a way to have tell matlab to automatically adjust the starting value with an if statement?

[Walter Roberson]

You can use try/catch but then you would need a search algorithm better than the one built in to fzero.

If you already have information about where a root might be, use that point the first time.

If not...

well imagine an upside-down Gaussian.... nearly flat except that in a narrow range it dips slightly below zero. Place that one dip somewhere between -realmax and +realmax. What search strategy are you going to use to find it?

Answer 2

[Ju DING]

well,I also encounter the same problem as you.Please check your function input, maybe there is an illegal input.