Python in a Nutshell

Name

diagonal

Synopsis

diagonal(a,k=0,axis1=0,axis2=1)

Returns the elements of a whose index along axis1 and index along axis2 differ by k. When a has rank 2, this means the main diagonal when k equals 0, subdiagonals above the main one when k is greater than 0, and subdiagonals below the main one when k is less than 0. For example:

# a is [[0 1 2 3]
#       [4 5 6 7]
#       [8 9 10 11]
#       [12 13 14 15]]
print Numeric.diagonal(a)        # prints: [0 5 10 15]
print Numeric.diagonal(a,1)      # prints: [1 6 11]
print Numeric.diagonal(a,-1)     # prints: [4 9 14]

As shown, diagonal( a ) is the main diagonal, diagonal( a ,1) the subdiagonal just above the main one, and diagonal( a ,-1) the subdiagonal just below the main one.