Search for a variable in a list of *.mat files
Inputs:
variable - The variable name to search for. Can be an exact name or just
the beginning of a name. In the latter case put a * at the end.
file filter - Filter for the file names to search (Optional). A .mat
is added to the filter if it does not already exist
Output:
If no output has been assigned, the function will print all the files
that contain the variable. Otherwise, a structure containing the file
name and the variable name is output.
Rezaul, 2004.