Node:Finding Elements and Checking Conditions, Next:Rearranging Matrices, Up:Matrix Manipulation
The functions any
and all
are useful for determining
whether any or all of the elements of a matrix satisfy some condition.
The find
function is also useful in determining which elements of
a matrix meet a specified condition.
any (x, dim) | Built-in Function |
For a vector argument, return 1 if any element of the vector is
nonzero.
For a matrix argument, return a row vector of ones and
zeros with each element indicating whether any of the elements of the
corresponding column of the matrix are nonzero. For example,
any (eye (2, 4)) => [ 1, 1, 0, 0 ] If the optional argument dim is supplied, work along dimension
dim. For example,
any (eye (2, 4), 2) => [ 1; 1 ] |
all (x, dim) | Built-in Function |
The function all behaves like the function any , except
that it returns true only if all the elements of a vector, or all the
elements along dimension dim of a matrix, are nonzero.
|
Since the comparison operators (see Comparison Ops) return matrices
of ones and zeros, it is easy to test a matrix for many things, not just
whether the elements are nonzero. For example,
all (all (rand (5) < 0.9)) => 0
tests a random 5 by 5 matrix to see if all of its elements are less than 0.9.
Note that in conditional contexts (like the test clause of if
and
while
statements) Octave treats the test as if you had typed
all (all (condition))
.
xor (x, y) | Mapping Function |
Return the `exclusive or' of the entries of x and y.
For boolean expressions x and y,
xor (x, y) is true if and only if x or y
is true, but not if both x and y are true.
|
is_duplicate_entry (x) | Function File |
Return non-zero if any entries in x are duplicates of one another. |
diff (x, k, dim) | Function File |
If x is a vector of length n, diff (x) is the
vector of first differences
x(2) - x(1), ..., x(n) - x(n-1).
If x is a matrix, The second argument is optional. If supplied, The dimension along which to take the difference can be explicitly
stated with the optional variable dim. In this case the
k-th order differences are calculated along this dimension.
In the case where k exceeds |
isinf (x) | Mapping Function |
Return 1 for elements of x that are infinite and zero
otherwise. For example,
isinf ([13, Inf, NA, NaN]) => [ 0, 1, 0, 0 ] |
isnan (x) | Mapping Function |
Return 1 for elements of x that are NaN values and zero
otherwise. For example,
isnan ([13, Inf, NA, NaN]) => [ 0, 0, 0, 1 ] |
finite (x) | Mapping Function |
Return 1 for elements of x that are finite values and zero
otherwise. For example,
finite ([13, Inf, NA, NaN]) => [ 1, 0, 0, 0 ] |
find (x) | Loadable Function |
Return a vector of indices of nonzero elements of a matrix. To obtain a
single index for each matrix element, Octave pretends that the columns
of a matrix form one long vector (like Fortran arrays are stored). For
example,
find (eye (2)) => [ 1; 4 ] If two outputs are requested, [i, j] = find (2 * eye (2)) => i = [ 1; 2 ] => j = [ 1; 2 ] If three outputs are requested, [i, j, v] = find (3 * eye (2)) => i = [ 1; 2 ] => j = [ 1; 2 ] => v = [ 3; 3 ] |
[err, y1, ...] = common_size (x1, ...) | Function File |
Determine if all input arguments are either scalar or of common
size. If so, err is zero, and yi is a matrix of the
common size with all entries equal to xi if this is a scalar or
xi otherwise. If the inputs cannot be brought to a common size,
errorcode is 1, and yi is xi. For example,
[errorcode, a, b] = common_size ([1 2; 3 4], 5) => errorcode = 0 => a = [ 1, 2; 3, 4 ] => b = [ 5, 5; 5, 5 ] This is useful for implementing functions where arguments can either be scalars or of common size. |