How to write a row of a matrix using if statement?

I have a Matrix M :-

M= (A    B)
A=1+x1+y1+x1y1

and

B=1+x2+y2+x2y2

How to write the B using if statement? Below is my code where i write A but don't know how to continue with B. Please help.

M=zeros([100,10]);
for i=1:100
     for j=1:20
         if j==1
           M(i,j)=1;
        elseif j==2
           M(i,j)=x(i);
        elseif j==3
           M(i,j)=y(i);
        elseif j==4
           M(i,j)=x(i)*y(i);
        
       After this how to add B? 

Answer 1

[dpb]

A=[ones(size(x1) x1 y1 x1.*y1];
B=[ones(size(x2) x2 y2 x2.*y2];
M=[A B];

Of course, numel(x1)==numel(x2) or all goes boom!