Method
save(filename,'-struct','S')
And then, exactly as the load documentation says, you can load the variables by supplying their names as optional arguments. E.g. if the mat file contains variables X and Y:
S = load(filename,'X','Y');
This will only load X and Y into the structure S, not matter what other variables are also present in the mat file.
Example
>> S.X = 1:3;
>> S.Y = 4:5;
>> S.Z = 6:9;
>> save('test.mat','-struct','S')
>> clear
>> S = load('test.mat','X','Y');
>> fieldnames(S)
ans =
'X'
'Y'
>> S.Y
ans =
4 5
