How can I add variable amount of padding to each column in my matrix?

So suppose I have a matrix, which has 4 columns and 10 rows. (10 by 4). I want to introduce 1 zero at the beginning in column 1, 2 zeros at the beginning in column 2, 3 zeros at the beginning in column 3 and 4 zeros at the beginning in column 4. Is there a way to manipulate padarray to allow me to introduce variable number of zeros like this?

any help appreciated!!

Answer 1

[Jon]

Try

Apad = tril(A,-1)

[Zuha Yousuf]

Thanks so much!!!

[Jon]

Your welcome. I'm glad that worked for you.

[Zuha Yousuf]

I have an additional question, if you could help? So the problem with tril is that it simply replaces my existing values with 0. What if I just wanted to add a variable number of zeros at the beginning of every column of my matrix (the same way as before), without it replacing any of my values? Is that doable?

[Jon]

I am having trouble understanding what you are trying to do. All the columns of a matrix must have the same number of rows. So I'm not sure where you would like to put the variable number of zeros. You could make a cell array from the individual columns and pad those separately so they each have a different length.

I think it would be best if you could make a simple illustrative, numerical example of a starting matrix A and what you want to end up with.

[Zuha Yousuf]

Hi! Basically something like this:

[Zuha Yousuf]

Wait can you see that properly? I'm uploading it again.

[Jon]

Hi Zuha, Sorry I haven't been on MATLAB answers for awhile. Just saw your follow up question. Here's one way to do what you are asking. Maybe there is a clever way to vectorize this and avoid the loop, but I think this will do the job. Be well

% example matrix to be padded
A = [2 5 8 11 14 17 20 23;
    3 6 9 12 15 18 21 24;
    4 7 10 13 16 19 22 25];
disp(A)

% define padding
nPad = [0 1 2 1 1 2 0 1]% npad(k) specifies number of zeros to pad the kth column in A



%loop to pad each column
for k = 1:length(nPad)
    if nPad(k) > 0 % check if it needs padding
        A(1:nPad(k),k) = 0;
    end
end
disp(A)