By the looks of the question probably you want:
% if you want first columns with 2 and the other as 3 then
ones(100,2).*[2,3] % since 2016b
bsxfun(@times,ones(100,2),[2,3]) % prior 2016b
By basic indexing [if you want to feed in the 2 by 3 matrix to a 100 by 2 matrix] then:https://in.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html :
a=rand(2,3); % example
[m,n]=size(a);
b=zeros(100,2);
b(1:n,:)=a'
