changing a .mat file for SPM batch process

I am trying to change SPM preprocessing parameters stored in a .mat file. I've figured out MATLAB doesn't seem to allow changing the values within the cell (it gave me strange errors indicating that the entire file no longer existed when I tried to change them). What would be the easiest way to edit these variables?

Answer 1

[Walter Roberson]

If you are trying to change just one variable within a .mat that contains many variables, then one route is to use the -append flag at the time you save the revised variable: http://www.mathworks.com/help/matlab/ref/save.html

Note that this will cause the .mat file to get longer; the old variables will not get deleted when you use -append, they will just not be used.

Another approach is to use the matfile class, which will probably need you to use -v7.3 files.

[Victoria Klimaj]

I'm new to Matlab, so I have a few questions about how that would work-- I have a script that uses the variables in the .mat file that I was hoping to change. By appending variables to the .mat file, these references will have to change, correct? Is this just functioning the same way as adding information in a new row or column would? Will this also be the case if I'm using the matfile class?

Or does the appending happen within a cell, functioning to essentially replace the old variable while still keeping the old information?

Thanks for your help!

[Walter Roberson]

If you use save -append, then the entire variable is replaced; it does not append on to the end of a variable, and you cannot just replace one cell in the variable.

If you use matfile then what you can change is more flexible.