how do I create the below Matrix?

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Brian Nuttall
Brian Nuttall 2015-3-24
回答： Konstantinos Sofos 2015-3-24
please see the attached image i need to create a tridiagonal nxn matrix using the diag function. i know how to make it this way but thats not what is required.
>> A=[2 -1 0 0 0;-1 2 -1 0 0;0 -1 2 -1 0;0 0 -1 2 -1; 0 0 0 -1 2]
A =
2 -1 0 0 0
-1 2 -1 0 0
0 -1 2 -1 0
0 0 -1 2 -1
0 0 0 -1 2
  1 个评论
James Tursa
James Tursa 2015-3-24
"... not what is required."
Is this homework? Have you reviewed the doc on diag to see how to get values into the off-diagonals?

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Konstantinos Sofos
Konstantinos Sofos 2015-3-24
Hi,
As James wrote you:Have you reviewed the doc on diag to see how to get values into the off-diagonals?
Mathworks offers an excellent documentation for such topics with plenty of examples.
You could use this
function Out = mydiag(n)
%n size of matrix Out
Out= diag(-1*ones(1,n-1),-1) + diag(2*ones(1,n)) + diag(-1*ones(1,n-1),1);
end
>> mydiag(5)
ans =
2 -1 0 0 0
-1 2 -1 0 0
0 -1 2 -1 0
0 0 -1 2 -1
0 0 0 -1 2

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