How to vectorize this loop? Subsequental subtraction of columns within a matrix

I'm trying to vectorize the following loop:

a=rand(1000,100);

j=1;
k=2;
tic
for i=1:50;
    b(:,i)=a(:,j)-a(:,k);
    j=j+1;
    k=k+1'
end
toc

Is there any easier way to subsequently subtract an entire column from the previous column within a matrix?

Thanks, Charles

Answer 1

[the cyclist]

b = a(:,1:end-1) - a(:,2:end);

[Andrei Bobrov]

b = -diff(a,1,2);