A = [1 30 50; 1 40 20; 1 10 30; 1 20 10; 1 50 40];
b = [-81.3 -63.5 -57.0 -44.8 -80.7]';
c = A\b
x= [10:50];
y = [10:50];
[X, Y] = meshgrid(x,y);
Z = c(1)+c(2)*X+c(3)*Y;
mesh(X, Y, Z)
Z(1,1)
X=10;
Y=10;
Z = c(1)+c(2)*X+c(3)*Y
