Interleave two vectors

% By Peter J. Acklam
N=10000
v1 = 1:N;
v2 = 1:N-1;

   vi = zeros(1, 2*N-1);
   vi(1:2:end) = v1;
   vi(2:2:end) = v2;
% or
   vi = [ v1 ; v2 0 ];
   vi = vi(1:end-1);

Multiply every column of matrix X by another vector V

X = rand(1000,500);
V = rand(1,1000);

X2 = zeros(1000,500)
for k = 1:500
   X2(:,k) = V.*X(:,k);
end

X2 = zeros(1000,500)
X2 = diag(sparse(V))*X;

Reverse a vector

X(end:-1:1)

fliplr

Create a 1000 by 1000 vector fulls of 7s

X=7*ones(1000,1000);

X=repmat(7,1000,1000);

X(1:1000,1:1000)=7;