GNU Octave Manual Version 3by John W. Eaton, David Bateman, Søren Hauberg Paperback (6"x9"), 568 pages ISBN 095461206X RRP £24.95 ($39.95) |

## 16.2 Rearranging Matrices

__Function File:__**fliplr***(*`x`)- Return a copy of
`x`with the order of the columns reversed. For example,fliplr ([1, 2; 3, 4]) => 2 1 4 3

Note that

`fliplr`

only work with 2-D arrays. To flip N-d arrays use`flipdim`

instead.See also flipud, flipdim, rot90, rotdim

__Function File:__**flipud***(*`x`)- Return a copy of
`x`with the order of the rows reversed. For example,flipud ([1, 2; 3, 4]) => 3 4 1 2

Due to the difficulty of defining which axis about which to flip the matrix

`flipud`

only work with 2-d arrays. To flip N-d arrays use`flipdim`

instead.See also fliplr, flipdim, rot90, rotdim

__Function File:__**flipdim***(*`x`,`dim`)- Return a copy of
`x`flipped about the dimension`dim`. For exampleflipdim ([1, 2; 3, 4], 2) => 2 1 4 3

See also fliplr, flipud, rot90, rotdim

__Function File:__**rot90***(*`x`,`n`)- Return a copy of
`x`with the elements rotated counterclockwise in 90-degree increments. The second argument is optional, and specifies how many 90-degree rotations are to be applied (the default value is 1). Negative values of`n`rotate the matrix in a clockwise direction. For example,rot90 ([1, 2; 3, 4], -1) => 3 1 4 2

rotates the given matrix clockwise by 90 degrees. The following are all equivalent statements:

rot90 ([1, 2; 3, 4], -1) rot90 ([1, 2; 3, 4], 3) rot90 ([1, 2; 3, 4], 7)

Due to the difficulty of defining an axis about which to rotate the matrix

`rot90`

only work with 2-D arrays. To rotate N-d arrays use`rotdim`

instead.See also rotdim, flipud, fliplr, flipdim

__Function File:__**rotdim***(*`x`,`n`,`plane`)- Return a copy of
`x`with the elements rotated counterclockwise in 90-degree increments. The second argument is optional, and specifies how many 90-degree rotations are to be applied (the default value is 1). The third argument is also optional and defines the plane of the rotation. As such`plane`is a two element vector containing two different valid dimensions of the matrix. If`plane`is not given Then the first two non-singleton dimensions are used.Negative values of

`n`rotate the matrix in a clockwise direction. For example,rotdim ([1, 2; 3, 4], -1, [1, 2]) => 3 1 4 2

rotates the given matrix clockwise by 90 degrees. The following are all equivalent statements:

rotdim ([1, 2; 3, 4], -1, [1, 2]) rotdim ([1, 2; 3, 4], 3, [1, 2]) rotdim ([1, 2; 3, 4], 7, [1, 2])

See also rot90, flipud, fliplr, flipdim

__Built-in Function:__**cat***(*`dim`,`array1`,`array2`, ...,`arrayN`)- Return the concatenation of N-d array objects,
`array1`,`array2`, ...,`arrayN`along dimension`dim`.A = ones (2, 2); B = zeros (2, 2); cat (2, A, B) => ans = 1 1 0 0 1 1 0 0

Alternatively, we can concatenate

`A`and`B`along the second dimension the following way:[A, B].

`dim`can be larger than the dimensions of the N-d array objects and the result will thus have`dim`dimensions as the following example shows:cat (4, ones(2, 2), zeros (2, 2)) => ans = ans(:,:,1,1) = 1 1 1 1 ans(:,:,1,2) = 0 0 0 0

See also horzcat, vertcat

__Built-in Function:__**horzcat***(*`array1`,`array2`, ...,`arrayN`)- Return the horizontal concatenation of N-d array objects,
`array1`,`array2`, ...,`arrayN`along dimension 2.See also cat, vertcat

__Built-in Function:__**vertcat***(*`array1`,`array2`, ...,`arrayN`)- Return the vertical concatenation of N-d array objects,
`array1`,`array2`, ...,`arrayN`along dimension 1.See also cat, horzcat

__Built-in Function:__**permute***(*`a`,`perm`)- Return the generalized transpose for an N-d array object
`a`. The permutation vector`perm`must contain the elements`1:ndims(a)`

(in any order, but each element must appear just once).See also ipermute

__Built-in Function:__**ipermute***(*`a`,`iperm`)- The inverse of the
`permute`

function. The expressionipermute (permute (a, perm), perm)

returns the original array

`a`.See also permute

__Built-in Function:__**reshape***(*`a`,`m`,`n`, ...)__Built-in Function:__**reshape***(*`a`,`size`)- Return a matrix with the given dimensions whose elements are taken
from the matrix
`a`. The elements of the matrix are accessed in column-major order (like Fortran arrays are stored).For example,

reshape ([1, 2, 3, 4], 2, 2) => 1 3 2 4

Note that the total number of elements in the original matrix must match the total number of elements in the new matrix.

A single dimension of the return matrix can be unknown and is flagged by an empty argument.

__Function File:__`y`=**circshift***(*`x`,`n`)- Circularly shifts the values of the array
`x`.`n`must be a vector of integers no longer than the number of dimensions in`x`. The values of`n`can be either positive or negative, which determines the direction in which the values or`x`are shifted. If an element of`n`is zero, then the corresponding dimension of`x`will not be shifted. For examplex = [1, 2, 3; 4, 5, 6; 7, 8, 9]; circshift (x, 1) => 7, 8, 9 1, 2, 3 4, 5, 6 circshift (x, -2) => 7, 8, 9 1, 2, 3 4, 5, 6 circshift (x, [0,1]) => 3, 1, 2 6, 4, 5 9, 7, 8

See also permute, ipermute, shiftdim

__Function File:__`y`=**shiftdim***(*`x`,`n`)__Function File:__[`y`,`ns`] =**shiftdim***(*`x`)- Shifts the dimension of
`x`by`n`, where`n`must be an integer scalar. When`n`is positive, the dimensions of`x`are shifted to the left, with the leading dimensions circulated to the end. If`n`is negative, then the dimensions of`x`are shifted to the right, with`n`leading singleton dimensions added.Called with a single argument,

`shiftdim`

, removes the leading singleton dimensions, returning the number of dimensions removed in the second output argument`ns`.For example

x = ones (1, 2, 3); size (shiftdim (x, -1)) => [1, 1, 2, 3] size (shiftdim (x, 1)) => [2, 3] [b, ns] = shiftdim (x); => b = [1, 1, 1; 1, 1, 1] => ns = 1

See also reshape, permute, ipermute, circshift, squeeze

__Function File:__**shift***(*`x`,`b`)__Function File:__**shift***(*`x`,`b`,`dim`)- If
`x`is a vector, perform a circular shift of length`b`of the elements of`x`.If

`x`is a matrix, do the same for each column of`x`. If the optional`dim`argument is given, operate along this dimension

__Loadable Function:__[`s`,`i`] =**sort***(*`x`)__Loadable Function:__[`s`,`i`] =**sort***(*`x`,`dim`)__Loadable Function:__[`s`,`i`] =**sort***(*`x`,`mode`)__Loadable Function:__[`s`,`i`] =**sort***(*`x`,`dim`,`mode`)- Return a copy of
`x`with the elements arranged in increasing order. For matrices,`sort`

orders the elements in each column.For example,

sort ([1, 2; 2, 3; 3, 1]) => 1 1 2 2 3 3

The

`sort`

function may also be used to produce a matrix containing the original row indices of the elements in the sorted matrix. For example,[s, i] = sort ([1, 2; 2, 3; 3, 1]) => s = 1 1 2 2 3 3 => i = 1 3 2 1 3 2

If the optional argument

`dim`is given, then the matrix is sorted along the dimension defined by`dim`. The optional argument`mode`

defines the order in which the values will be sorted. Valid values of`mode`

are `ascend' or `descend'.For equal elements, the indices are such that the equal elements are listed in the order that appeared in the original list.

The

`sort`

function may also be used to sort strings and cell arrays of strings, in which case the dictionary order of the strings is used.The algorithm used in

`sort`

is optimized for the sorting of partially ordered lists.

__Function File:__**sortrows***(*`a`,`c`)- Sort the rows of the matrix
`a`according to the order of the columns specified in`c`. If`c`is omitted, a lexicographical sort is used. By default ascending order is used however if elements of`c`are negative then the corresponding column is sorted in descending order.

Since the `sort`

function does not allow sort keys to be specified,
it can't be used to order the rows of a matrix according to the values
of the elements in various columns^{(7)}
in a single call. Using the second output, however, it is possible to
sort all rows based on the values in a given column. Here's an example
that sorts the rows of a matrix based on the values in the second
column.

a = [1, 2; 2, 3; 3, 1]; [s, i] = sort (a (:, 2)); a (i, :) => 3 1 1 2 2 3

__Function File:__**swap***(*`inputs`)-
[a1,b1] = swap(a,b) interchange a and b

__Function File:__**swapcols***(inputs)*-
function B = swapcols(A) permute columns of A into reverse order

__Function File:__**swaprows***(inputs)*-
function B = swaprows(A) permute rows of A into reverse order

__Function File:__**tril***(*`a`,`k`)__Function File:__**triu***(*`a`,`k`)- Return a new matrix formed by extracting the lower (
`tril`

) or upper (`triu`

) triangular part of the matrix`a`, and setting all other elements to zero. The second argument is optional, and specifies how many diagonals above or below the main diagonal should also be set to zero.The default value of

`k`is zero, so that`triu`

and`tril`

normally include the main diagonal as part of the result matrix.If the value of

`k`is negative, additional elements above (for`tril`

) or below (for`triu`

) the main diagonal are also selected.The absolute value of

`k`must not be greater than the number of sub- or super-diagonals.For example,

tril (ones (3), -1) => 0 0 0 1 0 0 1 1 0

and

tril (ones (3), 1) => 1 1 0 1 1 1 1 1 1

See also triu, diag

__Function File:__**vec***(*`x`)- Return the vector obtained by stacking the columns of the matrix
`x`one above the other.

__Function File:__**vech***(*`x`)- Return the vector obtained by eliminating all supradiagonal elements of
the square matrix
`x`and stacking the result one column above the other.

__Function File:__**prepad***(*`x`,`l`,`c`)__Function File:__**postpad***(*`x`,`l`,`c`)__Function File:__**postpad***(*`x`,`l`,`c`,`dim`)-
Prepends (appends) the scalar value

`c`to the vector`x`until it is of length`l`. If the third argument is not supplied, a value of 0 is used.If

`length (`

, elements from the beginning (end) of`x`) >`l``x`are removed until a vector of length`l`is obtained.If

`x`is a matrix, elements are prepended or removed from each row.If the optional

`dim`argument is given, then operate along this dimension.

__Function File:__**blkdiag***(*`a`,`b`,`c`, ...)- Build a block diagonal matrix from
`a`,`b`,`c`, .... All the arguments must be numeric and are two-dimensional matrices or scalars.See also diag, horzcat, vertcat

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