The colon is one of the most useful operators in MATLAB®.It can create vectors, subscript arrays, & specify for iterations.

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x = j:k createsa unit-spaced vector x with elements where m= fix(k-j). If j và k areboth integers, then this is simply .


x = j:i:k createsa regularly-spaced vector x using i asthe increment between elements. The vector elements are roughly equalto where m = fix((k-j)/i).However, if i is not an integer, then floatingpoint arithmetic plays a role in determining whether colon includesthe endpoint k in the vector, since k mightnot be exactly equal lớn j+m*i.If you specify nonscalar arrays, then MATLAB interprets j:i:k as j(1):i(1):k(1).


x = colon(j,k) and x = colon(j,i,k) arealternate ways to execute the commands j:k và j:i:k,but are rarely used. These syntaxes enable operator overloading forclasses.


A(:,n), A(m,:), A(:),and A(j:k) are common indexing expressions fora matrix A that contain a colon. When you use acolon as a subscript in an indexing expression, such as A(:,n),it acts as shorthand to include all subscriptsin a particular array dimension. It is also common lớn create a vectorwith 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 the nthcolumn of matrix A.

A(m,:) is the mthrow of matrix A.

A(:,:,p) is the pthpage of three-dimensional array A.

A(:) reshapes all elements of A intoa single column vector. This has no effect if A isalready a column vector.

A(:,:) reshapes all elements of A intoa two-dimensional matrix. This has no effect if A isalready a matrix or vector.

A(j:k) uses the vector j:k toindex into A và is therefore equivalent to thevector .

A(:,j:k) includes all subscriptsin the first dimension but uses the vector j:k toindex in the second dimension. This returns a matrix with columns .


Examples


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Create Unit-Spaced Vector


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Create a unit-spaced vector of numbers between 1 and 10. The colon operator uses a default increment of +1.


x = 1:10
x = 1×10 1 2 3 4 5 6 7 8 9 10

Create Vector with Specified Increment


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Create vectors that increment or decrement by a specified value.

Create a vector whose elements increment by 0.1.


x = 0:0.1:1
x = 1×11 0 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1.0000
Create a vector whose elements decrement by -2.


y = 10:-2:0
y = 1×6 10 8 6 4 2 0

Index Matrix Rows & Columns


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Examine several ways khổng lồ index a matrix using a colon :.

Create a 3-by-3 matrix. Index the first row.


A = magic(3)
A = 3×3 8 1 6 3 5 7 4 9 2
A(1,:)
ans = 1×3 8 1 6
Index the second & third column.


A(:,2:3)
ans = 3×2 1 6 5 7 9 2
Reshape the matrix into a column vector.


A(:)
ans = 9×1 8 3 4 1 5 9 6 7 2

Specify for-loop Iterations


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In the context of a for-loop, the colon specifies the loop iterations.

Write a for-loop that squares a number for values of n between 1 & 4.


for n = 1:4 n^2end
ans = 1
ans = 4
ans = 9
ans = 16

Input Arguments


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j — Starting vector value scalar


Starting vector value, specified as a real numeric scalar. If j so that the đầu ra vector is not empty, then j isthe first element in the vector.

Example: x = 0:5

Example: x= 0:0.5:5

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | char | datetime | duration


k — Ending vector value scalar


Ending vector value, specified as a real numeric scalar. K isthe last value in the vector only when the increment lines up to exactlyland on k. For example, the vector 0:5 includes5 as the last value, but 0:0.3:1 does not includethe value 1 as the last value since the increment does not line upwith the endpoint.

Example: x = 0:5

Example: x= 0:0.5:5

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | char | datetime | duration


i — Increment between vector elements 1 (default) | scalar


Increment between vector elements, specified as a real numericscalar.

Example: x = 0:0.5:5

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | char | datetime | duration


Output Arguments


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x — Regularly-spaced vector row vector


Regularly-spaced vector, returned as a row vector. If j> k, then x = j:k is an empty matrix.More generally, the syntax x = j:i:k returns anempty matrix when:


i, j, or k isan empty input

i == 0

i > 0 and j > k

i and j


Tips


Extended Capabilities


Tall Arrays Calculate with arrays that have more rows than fit in memory.


This function supports tall arrays with some limitations. Formore information, see Index and View Tall Array Elements.


C/C++ Code Generation Generate C và C++ code using MATLAB® Coder™.


Usage notes và limitations:


Complex inputs are not supported.

The đầu vào i cannot have a logicalvalue.

Vector inputs are not supported.

Inputs must be constants.

Uses single-precision arithmetic lớn produce single-precisionresults.


Thread-Based Environment Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.


This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.


GPU Arrays Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.


Usage notes & limitations:


To run this function on a GPU and obtain a gpuArray output, use any of the following syntaxes:
x = gpuArray.colon(j,k)x = gpuArray.colon(j,i,k)

Alternatively, you can also pass gpuArray objects directly to the colon operator:
x = gpuArray(j):gpuArray(k)x = gpuArray(j):gpuArray(i):gpuArray(k)

64-bit integers are not supported.


For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).


Distributed Arrays Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.


This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).


Version History


Introduced before R2006a

See Also

for | linspace | logspace | reshape | varargin


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