Matlab learning notes (4) matlab array

Catalog

MATLAB Array

MATLAB Special arrays in

MATLAB Rubik's cube matrix

MATLAB Multidimensional arrays

Detailed examples

MATLAB Array function

Detailed examples

MATLAB Array sorting

MATLAB Cell array

Be careful

Detailed examples

MATLAB Array access data on cells

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MATLAB Array

stay MATLAB Variables of all data types in are multidimensional arrays , A vector is a one-dimensional array , A matrix is a two-dimensional array .

First introduce some special arrays .

MATLAB Special arrays in

MATLAB We will use some functions to build some special arrays , For all these functions , A parameter creates a square array , Create a rectangular array with two parameters .

Use zeros()  Function to create an array with zero elements ：

for example ：

zeros(5)

MATLAB Execute the above instructions , Return the following results ：

Generate a 5 * 5 Of all the 0 matrix .

ans =
      0  0  0  0  0 
      0  0  0  0  0 
      0  0  0  0  0 
      0  0  0  0  0 
      0  0  0  0  0

Use ones()  function Create an array ：

for example ：

ones(4,3)

MATLAB Execute the above instructions , Return the following results ：

Generate a 4 * 3 Of all the 1 matrix .

ans = 
     1 1 1
     1 1 1
     1 1 1
     1 1 1

Use eye()  function Create a matrix ：

for example ：

eye(4)

MATLAB Execute the above instructions , Return the following results ：

Generate a 4 * 4 Diagonal matrix of , As the name suggests, it is , At the opposite corners are 1, Related concepts need to be based on linear algebra .

ans = 
    1 0 0 0 
    0 1 0 0 
    0 0 1 0 
    0 0 0 1

Use rand() function Create an array （0,1） A random number that is uniformly distributed on a graph ：

for example ：

rand(3, 5)

MATLAB Execute the above instructions , Return the following results ：

ans = 
     0.8147  0.9134  0.2785  0.9649  0.9572 
     0.9058  0.6324  0.5469  0.1576  0.4854 
     0.1270  0.0975  0.9575  0.9706  0.8003

MATLAB Rubik's cube matrix

Produce the same sum , When its elements are added line by line , A column by column or diagonal cube is a square .

Use magic()  function Create a magic cube array , It needs a singular Parameters of , This parameter Must be a greater than or equal to 3 scalar .

for example ：

magic(4)

MATLAB Execute the above instructions , Return the following results ：

The resulting matrix can be found , Any line 、 Any column 、 The sum of any diagonal number is 34, This is the magic cube matrix .

ans = 
      16 2   3  13 
      5  11  10 8 
      9  7   6  12 
      4  14  15 1

MATLAB Multidimensional arrays

stay MATLAB in , An array with more than two dimensions is called a multidimensional array .

stay MATLAB The multidimensional array in is an extension of the normal two-dimensional matrix .

MATLAB You need to create a two-dimensional array and then extend it , In this way, a multidimensional array can be generated .

for example , Let's first create a two-dimensional array a.

a = [7 9 5; 6 1 9; 4 3 2]

MATLAB Execute the above instructions , Return the following results ：

a =
     7     9     5
     6     1     9
     4     3     2

Array a It's a 3x3 array , By the value provided , We can add a third dimension , for example ：

a(:, :, 2)= [ 1 2 3; 4 5 6; 7 8 9]

MATLAB Execute the above instructions , Return the following results ：

a(:,:,1) =
     7     9     5
     6     1     9
     4     3     2

a(:,:,2) =
     1     2     3
     4     5     6
     7     8     9

Again , We can also use  ones(), zeros() or rand()  Function to create a multidimensional array .

for example ：

b = rand(4,3,2)

MATLAB Execute the above instructions , Return the following results ：

b(:,:,1) =
    0.0344    0.7952    0.6463
    0.4387    0.1869    0.7094
    0.3816    0.4898    0.7547
    0.7655    0.4456    0.2760

b(:,:,2) =
    0.6797    0.4984    0.2238
    0.6551    0.9597    0.7513
    0.1626    0.3404    0.2551
    0.1190    0.5853    0.5060

Can also use cat() function To create a multidimensional array , It combines a list of arrays along a specified dimension ：

cat() The syntax of the function is ：

B = cat(dim, A1, A2...)

Be careful ：

• B  Is a new array ;

• A1, A2, ... Is the array to be connected ;

• dim  Is the dimension of a series array .

Detailed examples

stay MATLAB Create a script file in , Enter the following code ：

a = [9 8 7; 6 5 4; 3 2 1];
b = [1 2 3; 4 5 6; 7 8 9];
c = cat(3, a, b, [ 2 3 1; 4 7 8; 3 9 0])

When running this command , Show results ：

The matrix a And matrices b Spliced with another unnamed matrix , Form a three-dimensional matrix .

c(:,:,1) =
     9     8     7
     6     5     4
     3     2     1
c(:,:,2) =
     1     2     3
     4     5     6
     7     8     9
c(:,:,3) =
     2     3     1
     4     7     8
     3     9     0

MATLAB Array function

MATLAB The following functions are provided for sorting , rotate , Chaos , Reshape or move the contents of an array .

function	Purpose
length	Vector length or maximum array size
ndims	Array dimensions
numel	The number of array elements
size	Array dimensions
iscolumn	Determines whether the input is a column vector
isempty	Determines whether the array is empty
ismatrix	Determines whether the input is a matrix
isrow	Determines whether the input is a line vector
isscalar	Determines whether the input is scalar
isvector	Determines whether the input is a vector
blkdiag	Construct block diagonal matrix from input parameters
circshift	Cyclic shift
ctranspose	Complex conjugate transpose
diag	Diagonal matrix and diagonal of matrix
flipdim	Flips the array along the specified dimension
fliplr	Flip the matrix from left to right
flipud	Flip the matrix down
ipermute	n- The inverse permutation dimension of a dimensional array
permute	Rearrange N Dimension of dimension group
repmat	Copy and tile arrays
reshape	Reshape the array
rot90	Rotation matrix 90 degree
shiftdim	Shift dimension
issorted	Determines whether the collection elements are arranged in sort order
sort	Sort the array elements in ascending or descending order
sortrows	Sort rows in ascending order
squeeze	Delete a single dimension
transpose	Transposition
vectorize	Vectorization expression

Detailed examples

Some of the above functions will be illustrated by the following examples .

length , Elements of size and quantity ：

stay MATLAB Create a script file in , Enter the following code ：

x = [7.1, 3.4, 7.2, 28/4, 3.6, 17, 9.4, 8.9];
length(x)  %  Array  x  The length of 
y = rand(3, 4, 5, 2);
ndims(y)   %  Array  y  Dimensions 
s = ['Zara', 'Nuha', 'Shamim', 'Riz', 'Shadab'];
numel(s)   %  Array  s  Number of elements of 

Run the command , The following results are displayed ：

ans =
     8
ans =
     4
ans =
    23

Circularly shifted array elements ：

stay MATLAB Create a script file in , Enter the following code ：

a = [1 2 3; 4 5 6; 7 8 9] %  The original matrix  y
b = circshift(a,1)   %  The matrix loops down one row 
c = circshift(a,[1 -1]) %  The matrix moves down one row , Move one more column to the left  
                        

Run the command , The following results are displayed ：

a =
     1     2     3
     4     5     6
     7     8     9

b =
     7     8     9
     1     2     3
     4     5     6

c =
     8     9     7
     2     3     1
     5     6     4

MATLAB Array sorting

stay MATLAB Create a script file in , Enter the following code ：

v = [ 23 45 12 9 5 0 19 17]  % Horizontal array  v
sort(v)   % An array  v  Sort 
m = [2 6 4; 5 3 9; 2 0 1] %  Two dimensional array 
sort(m, 1)   %  Sort by row 
sort(m, 2)   %  Sort by column 

Run the command , The following results are displayed ：

v =
    23    45    12     9     5     0    19    17
ans =
     0     5     9    12    17    19    23    45
m =
     2     6     4
     5     3     9
     2     0     1
ans =
     2     0     1
     2     3     4
     5     6     9
ans =
     2     4     6
     3     5     9
     0     1     2

MATLAB Cell array

Each cell in the array of cell arrays can store index cells of arrays with different dimensions and data types .

The cell function is used to create a cell array .

The syntax of the cell function is as follows ：

C = cell(dim)
C = cell(dim1,...,dimN)
D = cell(obj)

Be careful

• C  Is a cell array ;

• dim  Is a scalar integer or an integer vector , Specify the cell array C The size of the ;

• dim1, ... , dimN  Is a scalar integer that specifies the size of C;

• obj  Is one of the following

  • Java Array or object

  • .NET array System.String Type or System.Object

Detailed examples

stay MATLAB Create a script file in , Enter the following code ：

c = cell(2, 5);
c = {'Red', 'Blue', 'Green', 'Yellow', 'White'; 1 2 3 4 5}

Run the command , The following results are displayed ：

c = 
    'Red'    'Blue'    'Green'    'Yellow'    'White'
    [  1]    [   2]    [    3]    [     4]    [    5]

MATLAB Array access data on cells

There are two ways to reference elements of a cell array ：

• The closed index is in the first  bracket (), Is a group of cells

• Enclosed in curly braces {}, Index the data in a single cell

Included in the index of the first bracket , It refers to the set of cells .

Cell array index stationary bracket cell set .

for example ：

c = {'Red', 'Blue', 'Green', 'Yellow', 'White'; 1 2 3 4 5};
c(1:2,1:2)

MATLAB Execute the above instructions , Return the following results ：

ans = 
    'Red'    'Blue'
    [  1]    [   2]

You can also use curly braces “{ }” The index accesses the contents of the cell .

for example ：

c = {'Red', 'Blue', 'Green', 'Yellow', 'White'; 1 2 3 4 5};
c{1, 2:4}

MATLAB Execute the above instructions , Return the following results ：

ans =
   Blue
ans =
   Green
ans =
   Yellow