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FreeMat
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Section: Array Generation and Manipulations
The diag function is used to either construct a diagonal matrix from a vector, or return the diagonal elements of a matrix as a vector. The general syntax for its use is
y = diag(x,n)
If x is a matrix, then y returns the n-th diagonal. If n is omitted, it is assumed to be zero. Conversely, if x is a vector, then y is a matrix with x set to the n-th diagonal.
Here is an example of diag being used to extract a diagonal from a matrix.
--> A = int32(10*rand(4,5)) A = 5 8 8 3 6 4 8 4 3 7 9 5 8 4 2 1 0 10 0 4 --> diag(A) ans = 5 8 8 0 --> diag(A,1) ans = 8 4 4 4
Here is an example of the second form of diag, being used to construct a diagonal matrix.
--> x = int32(10*rand(1,3)) x = 6 3 9 --> diag(x) ans = 6 0 0 0 3 0 0 0 9 --> diag(x,-1) ans = 0 0 0 0 6 0 0 0 0 3 0 0 0 0 9 0