colon, :
Vector creation, array subscripting, and for
-loop
iteration
Syntax
x = j:k x = j:i:k A(:,n) A(m,:) A(:) A(j:k)
Description
The colon is one of the most useful operators in MATLAB®.
It can create vectors, subscript arrays, and specify for
iterations.
creates a regularly-spaced vector x
= j
:i
:k
x
using
i
as the increment between elements. The vector elements
are roughly equal to [j,j+i,j+2*i,...,j+m*i]
where m
= fix((k-j)/i)
. However, if i
is not an
integer, then floating point arithmetic plays a role in determining whether
colon
includes the endpoint k
in the
vector, since k
might not be exactly
equal to j+m*i
.
x = colon(j,k)
and x = colon(j,i,k)
are
alternate ways to execute the commands j:k
and j:i:k
,
but are rarely used. These syntaxes enable operator overloading for
classes.
A(:,n)
, A(m,:)
, A(:)
,
and A(j:k)
are common indexing expressions for
a matrix A
that contain a colon. When you use a
colon as a subscript in an indexing expression, such as A(:,n)
,
it acts as shorthand to include all subscripts
in a particular array dimension. It is also common to create a vector
with a colon for the purposes of indexing, such as A(j:k)
.
Some indexing expressions combine both uses of the colon, as in A(:,j:k)
.
Common indexing expressions that contain a colon are:
A(:,n)
is then
th column of matrixA
.A(m,:)
is them
th row of matrixA
.A(:,:,p)
is thep
th page of three-dimensional arrayA
.A(:)
reshapes all elements ofA
into a single column vector. This has no effect ifA
is already a column vector.A(:,:)
reshapes all elements ofA
into a two-dimensional matrix. This has no effect ifA
is already a matrix or vector.A(j:k)
uses the vectorj:k
to index intoA
and is therefore equivalent to the vector[A(j), A(j+1), ..., A(k)]
.A(:,j:k)
includes all subscripts in the first dimension but uses the vectorj:k
to index in the second dimension. This returns a matrix with columns[A(:,j), A(:,j+1), ..., A(:,k)]
.
Examples
Input Arguments
Output Arguments
Tips
The
for
reference page has a description of how to use:
in the context of loop statements.linspace
is similar to the colon operator:
, but it gives direct control over the number of points and always includes the endpoints. The sibling functionlogspace
generates logarithmically spaced values.When you create a vector to index into a cell array or structure array (such as
orcellName
{:}
), MATLAB returns multiple outputs in a comma-separated list. For more information, see How to Use Comma-Separated Lists.structName
(:).fieldName