how do I create the below Matrix?

Question

Brian Nuttall 2015-3-24

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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

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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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Answer 1

Konstantinos Sofos 2015-3-24

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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