MATLAB快速入门——国外大神的教程-USB迷|专注于互联网分享

2024年3月6日发(作者：空绿兰)

MATLAB stands for MATrix LABoratory. It is a powerful numerical computing

language commonly used in engineering and mathematics.

If you have any feedback please feel free to reach me at @the_ozzinator,

or a@.

%% Code sections start with two percent signs. Section titles go on the same

line.

% Comments start with a percent sign.

Multi line comments look

something

this

% commands can span multiple lines, using '...':

a = 1+2+ ...

% commands can be passed to the operating system

!ping

who% Displays all variables in memory

whos% Displays all variables in memory, with their types

clear% Erases all your variables from memory

clear('A') % Erases a particular variable

openvar('A') % Open variable in variable editor

clc% Erases the writing on your Command Window

diary% Toggle writing Command Window text to file

ctrl-c % Abort current computation

edit('myfunction.m') % Open function/script in editor

type('myfunction.m') % Print the source of function/script to Command Window

profileon% turns on the code profiler

profileoff% turns off the code profiler

profile viewer % Open profiler

help command % Displays documentation for command in Command Window

doc command % Displays documentation for command in Help Window

lookfor command % Searches for command in the first commented line of all

functions

lookfor command -all% searches for command in all functions

% Output formatting

format short % 4 decimals in a floating number

format long % 15 decimals

format bank % only two digits after decimal point - for financial

calculations

fprintf('text') % print "text" to the screen

disp('text') % print "text" to the screen

% Variables & Expressions

myVariable = 4% Notice Workspace pane shows newly created variable

myVariable = 4; % Semi colon suppresses output to the Command Window

4+6% ans = 10

8* myVariable % ans = 32

2^3% ans = 8

a = 2; b = 3;

c = exp(a)*sin(pi/2) % c = 7.3891

% Calling functions can be done in either of two ways:

% Standard function syntax:

load('', 'y') % arguments within parentheses, separated by commas

% Command syntax:

load y % no parentheses, and spaces instead of commas

% Note the lack of quote marks in command form: inputs are always passed as

% literal text - cannot pass variable values. Also, can't receive output:

[V,D] = eig(A); % this has no equivalent in command form

[~,D] = eig(A); % if you only want D and not V

% Logicals

1>5% ans = 0

10>=10% ans = 1

3~=4% Not equal to -> ans = 1

3==3% equal to -> ans = 1

3>1&&4>1% AND -> ans = 1

3>1||4>1% OR -> ans = 1

~1 % NOT -> ans = 0

% Logicals can be applied to matrices:

A >5

% for each element, if condition is true, that element is 1 in returned matrix

A( A >5 )

% returns a vector containing the elements in A for which condition is true

% Strings

a = 'MyString'

length(a) % ans = 8

a(2) % ans = y

[a,a] % ans = MyStringMyString

% Cells

a = {'one', 'two', 'three'}

a(1) % ans = 'one' - returns a cell

char(a(1)) % ans = one - returns a string

% Structures

A.b = {'one','two'};

A.c = [12];

A.d.e = false;

% Vectors

x = [4325371]

x(2) % ans = 32, indices in Matlab start 1, not 0

x(2:3) % ans = 32 53

x(2:end) % ans = 32 53 7 1

x = [4; 32; 53; 7; 1] % Column vector

x = [1:10] % x = 1 2 3 4 5 6 7 8 9 10

x = [1:2:10] % Increment by 2, i.e. x = 1 3 5 7 9

% Matrices

A = [123; 456; 789]

% Rows are separated by a semicolon; elements are separated with space or comma

% A =

% 1 2 3

% 4 5 6

% 7 8 9

A(2,3) % ans = 6, A(row, column)

A(6) % ans = 8

% (implicitly concatenates columns into vector, then indexes into that)

A(2,3) = 42% Update row 2 col 3 with 42

% A =

% 1 2 3

% 4 5 42

% 7 8 9

A(2:3,2:3) % Creates a new matrix from the old one

%ans =

% 5 42

% 8 9

A(:,1) % All rows in column 1

%ans =

% 1

% 4

% 7

A(1,:) % All columns in row 1

%ans =

% 1 2 3

[A ; A] % Concatenation of matrices (vertically)

%ans =

% 1 2 3

% 4 5 42

% 7 8 9

% 1 2 3

% 4 5 42

% 7 8 9

% this is the same as

vertcat(A,A);

[A , A] % Concatenation of matrices (horizontally)

%ans =

% 1 2 3 1 2 3

% 4 5 42 4 5 42

% 7 8 9 7 8 9

% this is the same as

horzcat(A,A);

A(:, [312]) % Rearrange the columns of original matrix

%ans =

% 3 1 2

% 42 4 5

% 9 7 8

size(A) % ans = 3 3

A(1, :) =[] % Delete the first row of the matrix

A(:, 1) =[] % Delete the first column of the matrix

transpose(A) % Transpose the matrix, which is the same as:

A one

ctranspose(A) % Hermitian transpose the matrix

% (the transpose, followed by taking complex conjugate of each element)

A'% Concise version of complex transpose

A.'% Concise version of transpose (without taking complex conjugate)

% Element by Element Arithmetic vs. Matrix Arithmetic

% On their own, the arithmetic operators act on whole matrices. When preceded

% by a period, they act on each element instead. For example:

A * B % Matrix multiplication

A .* B % Multiple each element in A by its corresponding element in B

% There are several pairs of functions, where one acts on each element, and

% the other (whose name ends in m) acts on the whole matrix.

exp(A) % exponentiate each element

expm(A) % calculate the matrix exponential

sqrt(A) % take the square root of each element

sqrtm(A) % find the matrix whose square is A

% Plotting

x = 0:.10:2*pi; % Creates a vector that starts at 0 and ends at 2*pi with increments

of .1

y = sin(x);

plot(x,y)

xlabel('x axis')

ylabel('y axis')

title('Plot of y = sin(x)')

axis([02*pi -11]) % x range from 0 to 2*pi, y range from -1 to 1

plot(x,y1,'-',x,y2,'--',x,y3,':') % For multiple functions on one plot

legend('Line 1 label', 'Line 2 label') % Label curves with a legend

% Alternative method to plot multiple functions in one plot.

% while 'hold' is on, commands add to existing graph rather than replacing it

plot(x, y)

holdon

plot(x, z)

holdoff

loglog(x, y) % A log-log plot

semilogx(x, y) % A plot with logarithmic x-axis

semilogy(x, y) % A plot with logarithmic y-axis

fplot (@(x) x^2, [2,5]) % plot the function x^2 from x=2 to x=5

gridon% Show grid; turn off with 'grid off'

axissquare% Makes the current axes region square

axis equal % Set aspect ratio so data units are the same in every direction

scatter(x, y); % Scatter-plot

hist(x); % Histogram

stem(x); % Plot values as stems, useful for displaying discrete data

bar(x); % Plot bar graph

z = sin(x);

plot3(x,y,z); % 3D line plot

pcolor(A) % Heat-map of matrix: plot as grid of rectangles, coloured by value

contour(A) % Contour plot of matrix

mesh(A) % Plot as a mesh surface

h = figure% Create new figure object, with handle h

figure(h) % Makes the figure corresponding to handle h the current figure

close(h) % close figure with handle h

closeall% close all open figure windows

close% close current figure window

shg % bring an existing graphics window forward, or create new one if needed

clfclear% clear current figure window, and reset most figure properties

% Properties can be set and changed through a figure handle.

% You can save a handle to a figure when you create it.

% The function get returns a handle to the current figure

h = plot(x, y); % you can save a handle to a figure when you create it

set(h, 'Color', 'r')

% 'y' yellow; 'm' magenta, 'c' cyan, 'r' red, 'g' green, 'b' blue, 'w' white,

'k' black

set(h, 'LineStyle', '--')

% '--' is solid line, '---' dashed, ':' dotted, '-.' dash-dot, 'none' is no line

get(h, 'LineStyle')

% The function gca returns a handle to the axes for the current figure

set(gca, 'XDir', 'reverse'); % reverse the direction of the x-axis

% To create a figure that contains several axes in tiled positions, use subplot

subplot(2,3,1); % select the first position in a 2-by-3 grid of subplots

plot(x1); title('First Plot') % plot something in this position

subplot(2,3,2); % select second position in the grid

plot(x2); title('Second Plot') % plot something there

% To use functions or scripts, they must be on your path or current directory

path% display current path

addpath /path/to/dir% add to path

rmpath /path/to/dir% remove from path

cd /path/to/move/into % change directory

% Variables can be saved to .mat files

save('') % Save the variables in your Workspace

load('') % Load saved variables into Workspace

% M-file Scripts

% A script file is an external file that contains a sequence of statements.

% They let you avoid repeatedly typing the same code in the Command Window

% Have .m extensions

% M-file Functions

% Like scripts, and have the same .m extension

% But can accept input arguments and return an output

% Also, they have their own workspace (ie. different variable scope).

% Function name should match file name (so save this example as double_input.m).

% 'help double_input.m' returns the comments under line beginning function

functionoutput = double_input(x)

%double_input(x) returns twice the value of x

output = 2*x;

end

double_input(6) % ans = 12

% You can also have subfunctions and nested functions.

% Subfunctions are in the same file as the primary function, and can only be

% called by functions in the file. Nested functions are defined within another

% functions, and have access to both its workspace and their own workspace.

% If you want to create a function without creating a new file you can use an

% anonymous function. Useful when quickly defining a function to pass to

% another function (eg. plot with fplot, evaluate an indefinite integral

% with quad, find roots with fzero, or find minimum with fminsearch).

% Example that returns the square of it's input, assigned to the handle sqr:

sqr = @(x) x.^2;

sqr(10) % ans = 100

doc function_handle % find out more

% User input

a = input('Enter the value: ')

% Stops execution of file and gives control to the keyboard: user can examine

% or change variables. Type 'return' to continue execution, or 'dbquit' to exit

keyboard

% Reading in data (also xlsread/importdata/imread for excel/CSV/image files)

fopen(filename)

% Output

disp(a) % Print out the value of variable a

disp('Hello World') % Print out a string

fprintf% Print to Command Window with more control

% Conditional statements (the parentheses are optional, but good style)

if (a >15)

disp('Greater than 15')

elseif (a ==23)

disp('a is 23')

else

disp('neither condition met')

end

% Looping

% NB. looping over elements of a vector/matrix is slow!

% Where possible, use functions that act on whole vector/matrix at once

for k = 1:5

disp(k)

end

k = 0;

while (k <5)

k = k +1;

end

% Timing code execution: 'toc' prints the time since 'tic' was called

tic

A = rand(1000);

A*A*A*A*A*A*A;

toc

% Connecting to a MySQL Database

dbname = 'database_name';

username = 'root';

password = 'root';

driver = '';

dburl = ['jdbc:mysql://localhost:8889/' dbname];

javaclasspath(''); %xx depends on version,

download available at /downloads/connector/j/

conn = database(dbname, username, password, driver, dburl);

sql = ['SELECT * from table_name where id = 22'] % Example sql statement

a = fetch(conn, sql) %a will contain your data

% Common math functions

sin(x)

cos(x)

tan(x)

asin(x)

acos(x)

atan(x)

exp(x)

sqrt(x)

log(x)

log10(x)

abs(x) %If x is complex, returns magnitude

min(x)

max(x)

ceil(x)

floor(x)

round(x)

rem(x)

rand% Uniformly distributed pseudorandom numbers

randi % Uniformly distributed pseudorandom integers

randn% Normally distributed pseudorandom numbers

%Complex math operations

abs(x) % Magnitude of complex variable x

phase(x) % Phase (or angle) of complex variable x

real(x) % Returns the real part of x (i.e returns a if x = a +jb)

imag(x) % Returns the imaginary part of x (i.e returns b if x = a+jb)

conj(x) % Returns the complex conjugate

% Common constants

NaN

inf

% Solving matrix equations (if no solution, returns a least squares solution)

% The and / operators are equivalent to the functions mldivide and mrdivide

x=Ab % Solves Ax=b. Faster and more numerically accurate than using inv(A)*b.

x=b/A % Solves xA=b

inv(A) % calculate the inverse matrix

pinv(A) % calculate the pseudo-inverse

% Common matrix functions

zeros(m,n) % m x n matrix of 0's

ones(m,n) % m x n matrix of 1's

diag(A) % Extracts the diagonal elements of a matrix A

diag(x) % Construct a matrix with diagonal elements listed in x, and zeroes

elsewhere

eye(m,n) % Identity matrix

linspace(x1, x2, n) % Return n equally spaced points, with min x1 and max x2

inv(A) % Inverse of matrix A

det(A) % Determinant of A

eig(A) % Eigenvalues and eigenvectors of A

trace(A) % Trace of matrix - equivalent to sum(diag(A))

isempty(A) % Tests if array is empty

all(A) % Tests if all elements are nonzero or true

any(A) % Tests if any elements are nonzero or true

isequal(A, B) % Tests equality of two arrays

numel(A) % Number of elements in matrix

triu(x) % Returns the upper triangular part of x

tril(x) % Returns the lower triangular part of x

cross(A,B) % Returns the cross product of the vectors A and B

dot(A,B) % Returns scalar product of two vectors (must have the same length)

transpose(A) % Returns the transpose of A

fliplr(A) % Flip matrix left to right

flipud(A) % Flip matrix up to down

% Matrix Factorisations

[L, U, P] = lu(A) % LU decomposition: PA = LU,L is lower triangular, U is upper

triangular, P is permutation matrix

[P, D] = eig(A) % eigen-decomposition: AP = PD, P's columns are eigenvectors

and D's diagonals are eigenvalues

[U,S,V] = svd(X) % SVD: XV = US, U and V are unitary matrices, S has non-negative

diagonal elements in decreasing order

% Common vector functions

max% largest component

min% smallest component

length% length of a vector

sort% sort in ascending order

sum% sum of elements

prod% product of elements

mode% modal value

median% median value

mean% mean value

std% standard deviation

perms(x) % list all permutations of elements of x

find(x) % Finds all non-zero elements of x and returns their indexes, can use

comparison operators,

% i.e. find( x == 3 ) returns indexes of elements that are equal to 3

% i.e. find( x >= 3 ) returns indexes of elements greater than or equal to 3

% Classes

% Matlab can support object-oriented programming.

% Classes must be put in a file of the class name with a .m extension.

% To begin, we create a simple class to store GPS waypoints.

% Begin WaypointClass.m

classdefWaypointClass% The class name.

properties% The properties of the class behave like Structures

latitude

longitude

end

methods

% This method that has the same name of the class is the constructor.

functionobj = WaypointClass(lat, lon)

de = lat;

ude = lon;

end

% Other functions that use the Waypoint object

functionr = multiplyLatBy(obj, n)

r = n*[de];

end

% If we want to add two Waypoint objects together without calling

% a special function we can overload Matlab's arithmetic like so:

functionr = plus(o1,o2)

r = WaypointClass([de] +[de], ...

[ude]+[ude]);

end

% End WaypointClass.m

% We can create an object of the class using the constructor

a = WaypointClass(45.0, 45.0)

% Class properties behave exactly like Matlab Structures.

de = 70.0

ude = 25.0

% Methods can be called in the same way as functions

ans = multiplyLatBy(a,3)

% The method can also be called using dot notation. In this case, the object

% does not need to be passed to the method.

ans = lyLatBy(a,1/3)

% Matlab functions can be overloaded to handle objects.

% In the method above, we have overloaded how Matlab handles

% the addition of two Waypoint objects.

b = WaypointClass(15.0, 32.0)

c = a + b