how to catch unwanted NaN and Inf

I sometimes unknowingly generate values which are NaN and later on it may cause unexpected problems. I want to catch occurances of NaN or Inf without manually inserting isnan and isinf everywhere. When I use

dbstop if naninf

I have the following problem: dbstop will stop in all sorts of built-in matlab functions. But I only want dbstop to stop when it finds NaN or inf in a variable that is in the scope of the main function I wrote. How do I change this or is there an alternate way to catch unwanted occurances of NaN/inf? Thanks.

Answer 1

[Matt J]

If it's a particular variable you're interested in, you can set a conditional breakpoint using a dbstop syntax like

 dbstop in file if any(isnan(A(:))

Or you can set the breakpoint GUI-style in the MATLAB editor as described here http://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html#brqxeeu-234.

[Habib]

Matt, thanks for your answer. what if I have multiple functions and they call each other and I want to stop in any of my files a nan or inf occurs for any variable? without stoping in matlab builtin functions!

[Image Analyst]

I'd doubt you would stop in any built-in functions unless the input was already bad. Use the isnan() or isinf() functions, wherever you think you need to, to detect any nans or infs, and take action such as correct them or alert the user.

[Habib]

Image Analyst, please take a look at my own question about this subject: http://www.mathworks.com/matlabcentral/answers/75300-how-to-use-dbstop-if-naninf

[Habib]

Image Analyst, please take a look at my own question about this subject: http://www.mathworks.com/matlabcentral/answers/75300-how-to-use-dbstop-if-naninf

and I tried isinf() :

Warning: Breakpoint expression
'isinf()' resulted in an error. The
error was
  Error using ==> isinf
  Not enough input arguments.

[Matt J]

ISINF works like this:

    >> isinf([1,2,3, Inf, 4 5])

    ans =

         0     0     0     1     0     0

To find NaNs as well, best to use ~isfinite()

    >> ~isfinite([NaN,2,3, Inf, 4 -Inf])

    ans =

         1     0     0     1     0     1

[Image Analyst]

What do you want to do with them once you find (if you find) nans and infs? Set them to some other value? Remove them totally from the vector (shortening the vector)?

[Habib]

If the execution stops at a nan, I am able to see what caused that and I can repair it. I have functions calling functions and above all a fzero is utilized inside another fzero... . It is not easy to manually track everything to find possible nan/infs. I face errors by fzero, and it takes quite some time to realize that oh, it origins from a nan in value. You know sometimes returned error messages are missleading.

... I aksed a question yesterday and Matt J, tried my coed and apparently something is wrong with my Matlab installation. It causes dbstop if naninf doesnt work correctly. I have to reinstall or upgrade first.

[Ghaith Mustafa]

@Image Analyst I have the same problem and i want to set them to zero value. How can i do that