Appending variables to the Mat-File:
Appending to the file adds to what has been saved in a file, and is accomplished by using the -append option. For illustration, supposing that the variable mymat already has been stored in the file 'sess2.mat', this would append the variable x to the file:
>> save -append sess2 x
>> who -file sess2
Your variables are:
mymat x
Without identifying variable(s), just save -append would add all the variables from the Command Window to the file. Whenever this happens, when the variable is not in the file, it is appended. If there is a variable with similar name in the file, it is substituted by the present value from the Command Window.