# TDDD34 Programming with Applications in Engineering

### Matrixes in Matlab

This describes commands that manipulate matrixes in different ways. Observe that a vector in Matlab is really a one dimensional matrix (just one row).

### Functions and operators

```        :               Generate a vector. For example 1:5 generates
the vector [1 2 3 4 5]. If three values is
given the middle is interpreted as stride.
For example 1:2:6 generate the vector [1 3 5].
If given in place of an index it denotes the
entire row/column. Let for example
A = [1 2; 3 4] then A(:,2) denote the
column [2;4].

.*		Perform element by element multiplication.

./		Perform element by element division.

.^		Perform element by element exponentiation.

'		(apostrophe) Transpose a matrix.

find		Return a vector with the indexes where the
matrix elements are nonzero

all		Controls if all elements of the matrix are
nonzero.

any		Controls if at least one element in the matrix
is nonzero.

size		Returns the dimension of a matrix
(the result is a vector).

length		Returns the length of a vector or the length
of the longest side in a matrix
(thus a 2x3-matrix and a 3x2-matrix both yield 3)

numel		Returns the number of elements in the entire
matrix or vector.

eye		Generate a matrix with ones in the diagonal
and zeros elsewhere.

ones		Generates a vector filled with ones.

zeros		Generates a vector filled with zeros.

diag		Generate a matrix with the diagonal set
to the argument vector. For example
diag([1 1 1]) is the same as eye(3,3).
Returns the diagonal elements in the
argument matrix. For example diag(eye(3,3))
returns a vector with three ones.

fliplr		Flips a matrix in left/right direction.

flipud		Flips a matrix in up/down direction

reshape		Generates a m*n matrix from a vector with m
times n elements.

A(r, c)		Retrieves the element at position (r, c)
where r is the row and c the column.

A(2:5, 3:4)	Retrieve the submatrix limited by the corners at
A(2,3), A(2,4), A(5,3), A(5,4). (I.e. retrieve the
matrix created from intersection of rows 2,3,4,5
and columns 3,4.)

```

You may want to pay attention to the fact that many functions in Matlab accepts matrixes as arguments, even if you normally expect them to handle only ordinary numbers. The function is then performed separately on each element (in the general case). For example "sin" and "abs".

Page responsible: Erik Nilsson
Last updated: 2013-08-12