Solution
This is exactly what load does when it has an output variable: it loads into one structure, where each field is one of the variables that were saved in the .mat file. So when you save only one variable dataout, the output of load is a structure with one field: dataout (your structure, but it could be anything). You can access your structure in the usual way:
S = load('file.mat');
b = S.dataout;
Here is a complete working example of this:
>> old.a = 12.7;
>> old.b = NaN;
>> old.c = 999;
>> save('test.mat','old')
>> S = load('test.mat');
>> new = S.old; % <- yes, you need this line!
>> new.a
ans = 12.700
Alternative
As an alternative you can actually change the save call to get exactly the effect that you desire, by using the '-struct' option:
>> save('test.mat','-struct','old') % <- note -struct option
>> new = load('test.mat');
>> new.c
ans = 999
This simply places all of the fields of the input scalar structure as separate variables in the mat file. Read the help to know more.
