CODEWITHSUNDEEP
matlabvariables
tc88
tc88

Reputation: 321

At which lines in my MATLAB code a variable is accessed?

I am defining a variable in the beginning of my source code in MATLAB. Now I would like to know at which lines this variable effects something. In other words, I would like to see all lines in which that variable is read out. This wish does not only include all accesses in the current function, but also possible accesses in sub-functions that use this variable as an input argument. In this way, I can see in a quick way where my change of this variable takes any influence.

Is there any possibility to do so in MATLAB? A graphical marking of the corresponding lines would be nice but a command line output might be even more practical.

Upvotes: 0

Views: 78

Answers (1)

user2271770
user2271770

Reputation:

You may always use "Find Files" to search for a certain keyword or expression. In my R2012a/Windows version is in Edit > Find Files..., with the keyboard shortcut [CTRL] + [SHIFT] + [F].

The result will be a list of lines where the searched string is found, in all the files found in the specified folder. Please check out the options in the search dialog for more details and flexibility.

Later edit: thanks to @zinjaai, I noticed that @tc88 required that this tool should track the effect of the name of the variable inside the functions/subfunctions. I think this is:

  1. very difficult to achieve. The problem of running trough all the possible values and branching on every possible conditional expression is... well is hard. I think is halting-problem-hard.

  2. in 90% of the case the assumption that the output of a function is influenced by the input is true. But the input and the output are part of the same statement (assigning the result of a function) so looking for where the variable is used as argument should suffice to identify what output variables are affected..

There are perverse cases where functions will alter arguments that are handle-type (because the argument is not copied, but referenced). This side-effect will break the assumption 2, and is one of the main reasons why 1. Outlining the cases when these side effects take place is again, hard, and is better to assume that all of them are modified.

Some other cases are inherently undecidable, because they don't depend on the computer states, but on the state of the "outside world". Example: suppose one calls uigetfile. The function returns a char type when the user selects a file, and a double type for the case when the user chooses not to select a file. Obviously the two cases will be treated differently. How could you know which variables are created/modified before the user deciding?

In conclusion: I think that human intuition, plus the MATLAB Debugger (for run time), and the Find Files (for quick search where a variable is used) and depfun (for quick identification of function dependence) is way cheaper. But I would like to be wrong. :-)

Upvotes: 1

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