MATLAB: How to create a meshgrid padded with a triangle of zeros in the upper-right and lower-left corners

Question

I want to take a vector, and turn it into a matrix where the original vector appears in each column, but offset down by the column number, so that I end up with an upper and lower triangle of zeros. For example, if I start with the vector

>> a=1:7
a =
       1     2     3     4     5     6     7

I can turn this into a 7×4 matrix where a appears in each column by using the function meshgrid:

>> [~,b]=meshgrid(1:4,a)
b =
       1     1     1     1
       2     2     2     2
       3     3     3     3
       4     4     4     4
       5     5     5     5
       6     6     6     6
       7     7     7     7

But what I really want is for b to look like this:

b =
       1     0     0     0
       2     1     0     0
       3     2     1     0
       4     3     2     1
       5     4     3     2
       6     5     4     3
       7     6     5     4
       0     7     6     5
       0     0     7     6
       0     0     0     7

Is there an easy way to do this, without using a for loop, such as:

for h=4:-1:1
    b(1:h-1,h)=zeros(h-1,1);
    b(h:length(a)+h-1,h)=a;
    b(length(a)+h:length(a)+3,h)=zeros(4-h,1);
end

Thanks

Answer 1

You can use

toeplitz([1:7 0 0 0],[1 0 0 0])