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Usage:
Keywords:
matrix algebra, variables, combining variables
trilower(a) returns a matrix d of the same size and shape as a with
d[i,j] = a[i,j] for i >= j (on or below the diagonal) and d[i,j] = 0 for
i < j (above the diagonal). Variable a must be a matrix but need not be
square.
[1 5 9] [1 0 0]
For example, when a is [2 6 10] , trilower(a) is [2 6 0] .
[3 7 11] [3 7 11]
[4 8 12] [4 8 12]
When a has type CHARACTER, elements above the diagonal are sent to empty
strings ("") instead of 0's.
trilower(a,T) or trilower(a,pack:T) returns the lower triangle (elements
a[i,j] with i >= j) of a in packed form. Matrix a must be square, that
is, nrows(a) = ncols(b). For example, when
[1 4 7]
a = [2 5 8] ,
[3 6 9]
trilower(a) is vector(1, 2, 5, 3, 6, 9).
Note: keyword 'square' is not valid for trilower().
See also triupper(), triunpack(), qr().
Gary Oehlert
2003-01-15