Need Help making a nxn symmetric matrix

My symmetric matrix should look like

[1 0 0 0 0..n no. of zeroes;
 1 -2 1 0 0 0..n;
 0 1 -2 1 0 0 ..;
 for n no of rows]

[James Tursa]

Are the last two rows this?

0 ... 0 1 -2 1;
0 ... 0 0  0 1];

Or this?

0 ... 0 1 -2  1;
0 ... 0 0  1 -2];

Is this an n X n matrix or an n X n+1 matrix? It is not clear from your example what the matrix should really look like since your example is not symmetric (e.g., the (2,1) spot is not equal to the (1,2) spot)

Answer 1

[James Tursa]

Making a guess at what you really want, you could build it in pieces, e.g.,

n = size of matrix;
A = zeros(n);
A(1:n+1:end) = -2; % The diagonal
A(2:n+1:end) = 1; % The lower diagonal
A(n+1:n+1:end) = 1; % The upper diagonal
A(1,1) = 1; % Different value for the (1,1) spot.

An alternative method could employ the spdiags function to build the matrix.

[Nitesh Panchal]

Few twitches and it worked perfectly thank you

[Stephen23]

See my answer for a much simpler way to create this matrix.

Answer 2

[Stephen23]

Simply use toeplitz:

>> n = 6;
>> M = toeplitz([-2,1,zeros(1,n-2)]);
>> M(1) = 1; M(end) = 1
M =
     1     1     0     0     0     0
     1    -2     1     0     0     0
     0     1    -2     1     0     0
     0     0     1    -2     1     0
     0     0     0     1    -2     1
     0     0     0     0     1     1

[Nitesh Panchal]

It was pretty simple but harder to comprehend , i tried using this command but i couldnt figure it out , but thank you so much