Reshape error on Matlab I can't figure out? - matlab

Question

Trying to add a row and column of zeroes to a user inputted matrices, can't fin any way past the reshape error
n = input ('Please Enter Desired Number of Rows:');
disp (''); % User prompted to enter the desied rows for the matrices.
m = input ('Please Enter Desired Number of Columns:');
disp (''); % User prompted to enter the desired columns for the matrices.
for x = 1:n
for y = 1:m
p (x,y) = input ('Enter Matrice Values:');
end
end
p = reshape (p, n, m);
% Adding Row of Zeros
a = zeros (1,m+1)
% Adding Column of Zeros
b= zeros (n,1)
Output_Matrix = [p b; a]

Answer 1

You don't need to reshape, get the size of p that was input by the user using [m, n] = size(p) and create Output_Matrix that's one row and one column bigger. Set the first m rows and n columns to p. Finally don't forget to preallocate any arrays before accessing them.
% User prompted to enter the desied rows for the matrices.
m = input('Please Enter Desired Number of Rows: '); disp ('')
% User prompted to enter the desired columns for the matrices.
n = input('Please Enter Desired Number of Columns: '); disp ('')
p = zeros(m,n);
for x = 1:m
for y = 1:n
p(x,y) = input('Enter Matrice Values: ');
end
end
[m, n] = size(p);
Output_Matrix = zeros(m+1,n+1);
Output_Matrix(1:end-1,1:end-1) = p;
Output_Matrix =
1 2 3 0
4 5 6 0
7 8 9 0
0 0 0 0

Answer 2

If you have a p matrix from some previous code and you want to expand it, you can simply do this to get that extra row and column of 0's appended:
% p is pre-existing from some other code
p(end+1,end+1) = 0; % this appends extra row and column of 0's
But if you are building the p from scratch and know the desired size ahead of time, then Chris's comment about pre-allocating p to zeros(m+1,n+1) is probably the way to go.