x) |
[x]) |
False
if x is empty (i.e., len(x)
is zero)
and True
otherwise.
x) |
x) |
x) |
x[, start=0.0]) |
Matrices can be used as arguments to the list(),
tuple(), zip(), map(), and
filter() functions described in section 2.1 of the Python
Library Reference. list(A)
and tuple(A)
construct a list, respectively a tuple, from the elements of A.
zip(A,B,...)
returns a list of tuples,
with the ith tuple containing the ith elements of A,
B, ....
>>> from cvxopt.base import matrix >>> A = matrix([[-11., -5., -20.], [-6., -0., 7.]]) >>> B = matrix(range(6), (3,2)) >>> list(A) [-11.0, -5.0, -20.0, -6.0, 0.0, 7.0] >>> tuple(B) (0, 1, 2, 3, 4, 5) >>> zip(A,B) [(-11.0, 0), (-5.0, 1), (-20.0, 2), (-6.0, 3), (0.0, 4), (7.0, 5)]
map(f,A)
, where f is a function and A
is a matrix, returns a list constructed by applying f to each
element of A. Multiple arguments can be provided, for example,
as in map(f,A,B)
, if f is a function
with two arguments.
>>> A = matrix([[5, -4, 10, -7], [-1, -5, -6, 2], [6, 1, 5, 2], [-1, 2, -3, -7]]) >>> B = matrix([[4,-15, 9, -14], [-4, -12, 1, -22], [-10, -9, 9, 12], [-9, -7,-11, -6]]) >>> print matrix(map(max, A, B), (4,4)) # takes componentwise maximum 5 -1 6 -1 -4 -5 1 2 10 1 9 -3 -7 2 12 -6
filter(f,A)
, where f is a function and
A is a matrix, returns a list containing the elements of A
for which f is true.
>>> print filter(lambda x: x%2, A) # list of odd elements in A [5, -7, -1, -5, 1, 5, -1, -3, -7] >>> print filter(lambda x: -2 < x < 3, A) # list of elements between -2 and 3 [-1, 2, 1, 2, -1, 2]
It is also possible to iterate over matrix elements, as illustrated in the following example.
>>> A = matrix([[5, -3], [9, 11]]) >>> for x in A: print max(x,0) ... 5 0 9 11 >>> [max(x,0) for x in A] [5, 0, 9, 11]
The expression "x in A" returns True
if an element
of A is equal to x and False
otherwise.