Undefined function 'padarray' for input arguments of type 'uint8'.

I am doing the MATLAB for beginners in Coursera. I am supposed to blur the image provided. The code works when run in my PC but I am getting this error message on the assignment page.

Undefined function 'padarray' for input arguments of type 'uint8'.

Error in blur (line 3)

img_padded = padarray(img,[w w],0,'both');

function output = blur(img,w)
img = uint8(img);
img_padded = padarray(img,[w w],0,'both');
[row, col] = size(img_padded);
blurred = zeros (row, col);
    for ii = (1+w):(row-w)
        for jj = (1+w):(col-w)
            submatrix = zeros(2*w + 1, 2*w + 1);
            for kk = (ii-w):(ii+w)
                for ll = (jj-w):(jj+w)
                    submatrix (kk,ll) = img_padded (kk,ll);
                end
            end
            blurred (ii,jj) = sum (submatrix, 'all')/((2*w+1)^2);
        end
    end 
    output = blurred (w+1:row-w,w+1:col-w);
    output = uint8(output);
end

[Walter Roberson]

padarray() requires that the Image Processing Toolbox is installed and licensed.

[Myra Poblete]

Thank you for the prompt response Walter. I have padded the matrix on my own, which worked but failed in both tests.

function output = blur(img,w)
img = uint8(img);
[a b] = size(img);
img_padded = zeros(a+2*w, b+2*w);
img_padded(1+w:a+w, 1+w:b+w) = img;
[row, col] = size(img_padded);
blurred = zeros (row, col);
    for ii = (1+w):(row-w)
        for jj = (1+w):(col-w)
            submatrix = zeros(2*w + 1, 2*w + 1);
            for kk = (ii-w):(ii+w)
                for ll = (jj-w):(jj+w)
                    submatrix (kk,ll) = img_padded (kk,ll);
                end
            end
            blurred (ii,jj) = sum (submatrix, 'all')/((2*w+1)^2);
        end
    end 
    output = blurred (w+1:row-w,w+1:col-w);
    output = uint8(output);
end

[Walter Roberson]

>> blur(ones(10,10),3)

ans =

  10×10 uint8 matrix

   0   0   0   1   1   1   1   0   0   0
   0   1   1   1   1   1   1   1   1   0
   0   1   1   1   1   1   1   1   1   0
   1   1   1   1   1   1   1   1   1   1
   1   1   1   1   1   1   1   1   1   1
   1   1   1   1   1   1   1   1   1   1
   1   1   1   1   1   1   1   1   1   1
   0   1   1   1   1   1   1   1   1   0
   0   1   1   1   1   1   1   1   1   0
   0   0   0   1   1   1   1   0   0   0

It seems unlikely that an image that is all 1 should get blurred into something that contains some 0's.

However, you did not post the problem statement of what is to happen at the boundaries.