Reshaping a Matrix :: Data Structures (Programming)

Programming

Reshaping a Matrix

The following functions change the shape of a matrix.

Function
Description

reshape
Modify the shape of a matrix.

rot90
Rotate the matrix by 90 degrees.

fliplr
Flip the matrix about a vertical axis.

flipud
Flip the matrix about a horizontal axis.

flipdim
Flip the matrix along the specified direction.

transpose
Flip a matrix about its main diagonal, turning row vectors into column vectors and vice versa.

ctranspose
Transpose a matrix and replace each element with its complex conjugate.

Function	Description
`reshape`	Modify the shape of a matrix.
`rot90`	Rotate the matrix by 90 degrees.
`fliplr`	Flip the matrix about a vertical axis.
`flipud`	Flip the matrix about a horizontal axis.
`flipdim`	Flip the matrix along the specified direction.
`transpose`	Flip a matrix about its main diagonal, turning row vectors into column vectors and vice versa.
`ctranspose`	Transpose a matrix and replace each element with its complex conjugate.

Examples

Here are a few examples to illustrate some of the ways you can reshape matrices.

Reshaping a Matrix. Reshape 3-by-4 matrix A to have dimensions 2-by-6:

A = [1 4 7 10; 2 5 8 11; 3 6 9 12]
A =
    1    4    7    10
    2    5    8    11
    3    6    9    12

B = reshape(A, 2, 6)
B =
    1    3    5    7    9   11
    2    4    6    8   10   12

Transposing a Matrix. Transpose A so that the row elements become columns. You can use either the transpose function or the transpose operator (.') to do this:

B = A.'
B =
     1     2     3
     4     5     6
     7     8     9
    10    11    12

There is a separate function called ctranspose that performs a complex conjugate transpose of a matrix. The equivalent operator for ctranpose on a matrix A is A':

A = [1+9i 2-8i 3+7i; 4-6i 5+5i 6-4i]
A =
   1.0000 + 9.0000i   2.0000 -8.0000i   3.0000 + 7.0000i
   4.0000 -6.0000i   5.0000 + 5.0000i   6.0000 -4.0000i

B = A'
B =
   1.0000 -9.0000i   4.0000 + 6.0000i
   2.0000 + 8.0000i   5.0000 -5.0000i
   3.0000 -7.0000i   6.0000 + 4.0000i

Rotating a Matrix. Rotate the matrix by 90 degrees:

B = rot90(A)
B =
    10    11    12
     7     8     9
     4     5     6
     1     2     3

Flipping a Matrix. Flip A in a left-to-right direction:

B = fliplr(A)
B =
    10     7     4     1
    11     8     5     2
    12     9     6     3

Diminishing the Size of a Matrix Preallocating Memory