MATLAB 2018a stalls on undefined variables

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Douglas Cook
Douglas Cook on 31 Jul 2018
Edited: Adam Danz on 24 Apr 2020
MATLAB was running fine, but today it keeps hanging. I can replicate this error very reliably and I've been able to determine that the problem is caused by a undefined variable. Essentially, every time that MATLAB encounters an undefined variable (whether in function, script, or command line), it hangs at "Busy" instead of quickly producing the typical error, "Undefined function or variable."
A previous post on this issue is found here: But in my case, MATLAB hangs regardless of whether I use a local directory or my wifi is turned off or on. So it doesn't seem to be related to a network issue.
Version information:
MATLAB Version: (R2018a)
MATLAB License Number: ••••••
Operating System: Microsoft Windows 10 Pro Version 10.0 (Build 15063)
Java Version: Java 1.8.0_144-b01 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
Additional information:
I restarted MATLAB several times, with the same symptom each time. The problem is not encountered when using MATLAB 2017a on the same computer.
Adam Danz
Adam Danz on 31 Jul 2018
It could be due to your computer resetting the network connections as suggested here . In my case, I access a remove "z-drive" at work and when I take my laptop home an no longer have access to the z-drive, I get this problem. When I restart matlab it typically goes away. Also, when I turn off my wifi it typically goes away, too.

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Answers (2)

Jose on 27 Sep 2018
I do have the same problem. Adam system is not working for me. I am a Mac user. I lose a lot of time every day just with that. So sad...
  1 Comment
Adam Danz
Adam Danz on 22 Aug 2019
It somestimes doesn't work for me either. It's not so much of a solution as it is a bandaid that needs repeatedly addressed. I think this is one of Matlab's biggest issues and the problem has existed for years.

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Zachary Eilon
Zachary Eilon on 22 Aug 2019
I am also having this issue, having just updated to 2019a. It is very frustrating. Happens whenever I cd to a new directory in my external server. This "feature" of searching back through the history is absurd if it has this consequence.
Adam Danz
Adam Danz on 28 Aug 2019
It's not 100% clear to me either partially becaues it's not documented well (or at all?).
The search path has clear descriptions in the documentation as well as the command history. In addition to that, there's the Current Folder history which lists your history of cd(). Apparently starting around r2017b (?) when there is an undefined variable or function matlab searches through the current folder history. When there are paths to networks that no longer exist, it takes a very long time for matlab to throw the undefined var/func error (sometimes up to a minute just because there was a typo). I'd be happy for anyone to add more detail to that.

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