Oh, matlab is really a marvel!
If I work on the command line and input the three lines bellow, then matlab can use all 10 cores.
    load('teaa466.mat','aa');
    load('tebb466.mat','bb');
    ab=aa\bb(:,5);
But if I wrote these three lines into a function f_fit4()
Then I run this function f_fit4. Matlab can only use 1 core.
That is not the end:
If I run these four lines in command window:
    load('teaa466.mat','aa');
    load('tebb466.mat','bb');
    ab=aa\bb(:,5);
    f_fit4;
Both two process can use all 10 core!!!!!!!!!!

