clear
disp('Fit ax + by + cz to data via least squares')
A =[3     9    12;
     5     8    13;
     7     7    16;
     9     5    18;
    11     4    21;
    12     3    23;
    14     2    26;
    15     1    29]
pause
d = [1.5 2 2 2 1.5 1.5 1.5 1.5]'
pause
ls_sol = A\d
pause
disp('Approximate derivative of x = ax +by +cz')
disp('ls_sol(1)*x + ls_sol(2)*y +ls_sol(3)*y')