MATLAB Programming

Resizing and Reshaping Matrices
Resizing and Reshaping Matrices
You can easily enlarge or shrink the size of a matrix, modify its shape, or
rotate it about various axes. This section covers
• “Expanding the Size of a Matrix” on page 1-27
• “Diminishing the Size of a Matrix” on page 1-31
• “Reshaping a Matrix” on page 1-32
• “Preallocating Memory” on page 1-34
Expanding the Size of a Matrix
You can expand the size of any existing matrix as long as doing so does
not give the resulting matrix an irregular shape. (See “Keeping Matrices
Rectangular” on page 1-8). For example, you can vertically combine a 4-by-3
matrix and 7-by-3 matrix because all rows of the resulting matrix have the
same number of columns (3).
Twowaysofexpandingthesizeofanexistingmatrixare
• Concatenating new elements onto the matrix
• Storing to a location outside the bounds of the matrix
Note If you intend to expand the size of a matrix repeatedly over time
as it requires more room (usually done in a programming loop), it is
advisable to preallocate space for the matrix when you initially create it. See
“Preallocating Memory” on page 1-34.
Concatenating Onto the Matrix
Concatenation is most useful when you want to expand a matrix by adding
newelementsorblocksthatarecompatible in size with the original matrix.
This means that the size of all matrices being joined along a specific dimension
must be equal along that dimension. See “Concatenating Matrices” on page
1-7.
1-27