You should not save data in an m-file; a mat-file is the best way. I believe the problem is how you are loading the data. If you call
load('ppvalue.mat')
the variables saved in the file are created in the current workspace with their values as they were saved in the file. If, instead, you assign the output of the call to load to a variable as in
s1 = load('ppvalue.mat');
then s1 will be a scalar structure with one field for each variable saved in the mat-file. The field names will be the names of the original variables.
Your code above attempts to compute the mean of the struct s1, which is not defined. Instead, try
mu1 = mean(s1.varname)
where varname is the original name of the variable that was saved to the mat-file. To see what it is, just look at s1 in the command window.
