MATLAB: Do I receive the M-Lint warning “The value assigned to variable might be unused” when the variable name is used as an argument to SAVE

MATLAB

I have the following function:

function myFunction
saveme = test;
save('test.mat', 'saveme')

I receive an M-Lint warning that variable 'saveme' is unused, even though I have passed it to the SAVE function.

Best Answer

The reason for the warning message is that the variable name 'saveme' is being passed as a string input parameter to SAVE. MATLAB does not recognize that this string corresponds to the variable 'saveme' until it evaluates the SAVE function at runtime.

If you would like to prevent this M-Lint message from being displayed, type

       %#ok

at the end of the line that line that produces the warning. For example:

function myFunction
saveme = test; %#ok
save('test.mat', 'saveme')

Alternatively, you may use the command format syntax for SAVE:

save test.mat saveme

instead of the function syntax.

Related Solutions

MATLAB: How to append the data available in two mat files with some variables having the same name, into a single file

The attached MATLAB file "append_var.m" is an example of how you can achieve this functionality. Also download the two sample MAT files attached to execute this example. The process involves the following steps:

1. Load the first MAT file (matlab1.mat) and read all the variables into another variable, say “file1” (stored as STRUCT).

2. Next read all the variables in the second MAT file (matlab2.mat) into another variable, say “file2” using the WHOS command without actually loading them into the workspace.

3. Do a string compare to see which variables are common between the two MAT files. If there is a common variable name, save the variable in current MAT file to temp, and load the variable from the other MAT file into the workspace and append it to temp using the EVAL function. If not, at the end of the loop just load this variable into the workspace.

4. Finally, clear the unwanted variables and save the current set of variables in another MAT file (if needed) or just overwrite to another file and delete any unnecessary MAT files.

MATLAB: Saving a variable from a function with a different name

Simple: call that function with that variable name as its output argument:

var_name = A(X,Y);

will define var_name in the workspace where the function is being called. Passing arguments is the fastest, simplest and neatest way of passing variables between workspaces, and this is what MATLAB themselves recommend (see link below). Whatever you do, do not learn sloppy buggy programing by passing arguments using assignin or globals. Although beginners love using them, actually both of these methods make code slower and buggier.

http://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

The entire concept of functions is very similar to encapsulation, which is broken when you start passing variables willy-nilly in and out of their workspaces. It is a bad idea.

Best Answer

Related Solutions

MATLAB: How to append the data available in two mat files with some variables having the same name, into a single file

MATLAB: Saving a variable from a function with a different name

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