How do you generalize a function with matrix dimensions increasing?

This is the code I have. Is there any way to generalize the matrix A so it increases from a 1x1 to a 2x2 then a 3x3 and so on instead of writing out each matrix separately? I don't understand how to create a general code to create a matrix that increases as show below...

        SP = xlsread('Shift Factor Data',-1);
        SPj = SP(1:end);
        MCC = xlsread('Shift Factor Data',-1);
        MCCj = MCC(1:end);
        A1 = SPj(1,1);
        B1 = -MCCj(1,1);
        X1 = A1\B1;
        A2 = [SPj(1,1) 0; SPj(1,1) SPj(2,1)];
        B2 = [-MCCj(1,1); -MCCj(2,1)];
        X2 = A2\B2;
        A3 = [SPj(1,1) 0 0; SPj(1,1) SPj(2,1) 0; SPj(1,1) SPj(2,1) SPj(3,1)];
        B3 = [-MCCj(1,1); -MCCj(2,1); -MCCj(3,1)];
        X3 = A3\B3;
        A4 = [SPj(1,1) 0 0 0; SPj(1,1) SPj(2,1) 0 0; SPj(1,1) SPj(2,1) SPj(3,1) 0; SPj(1,1) SPj(2,1) SPj(3,1) SPj(4,1)];
        B4 = [-MCCj(1,1); -MCCj(2,1); -MCCj(3,1); -MCCj(4,1)];
        X4 = A4\B4
        [m,n] = size(A4);
        Abar = A4(:,1:n-1);
        Xbar = X4(1:n-1,:);
        X = (B4-(Abar*Xbar))/(A4(:,n));
        Shift_Factor = X(n,n)