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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

	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: 2012-08-07