写在最前面:
下定决心好好整理学习过的Lynda.com课程的笔记,在以前的学习过程中光是跟着视频学习,看似是学的很快,但是没有巩固,很快就忘记了。视频学习的一个弊病是不利于复习,而这恰恰是书本学习的强项,因为可以随心所欲的划重点,复习时可以剔除啰嗦的部分,只看重点。这也是我开始整理学习笔记的初衷,希望能一直坚持下去。Lynda.com是全英文学习网站,所以所有笔记内容都是英文,而关于自己的心得体会还有思考,以及个别生涩单词,我会用中文在文中予以标注,便于自己反复查看。
0.Introduction
What You Should Know
- How to install software on your operating system
- How to get your data into a text file, such as the comma-separated value(CSV) files generated by Excel and other database programs
- How to work with free software
1.Introducing Octave
Downloading Octave
- http://www.sourceforge.net
- search for "octave"
- For Mac OS X:
- Go to www.octave.org
- Find the link Octave Wiki
Running Octave
octave:1> a = 3
a = 3
octave:2> b = a
b = 3
octave:3> PS1 <'>>'>;
>> exit % close octave
Getting help
>> help help
>> help pi
>> doc % press Ctrl + C to leave DOC
Support/Help: https://www.gnu.org/software/octave/support.html
Online doc: https://octave.org/doc/interpreter/
PDF: https://octave.org/octave.pdf
2.Surveying Basic Octave Commands
01. Using build-in commands
>> pi
ans = 3.1416
>> format long
>> pi
ans = 3.14159265358979
>> format short
>> pi
ans = 3.1416
>> a = pi
a = 3.1416
>> b = pi;
>> disp(a)
3.1416
>> c = rand()
c = 0.27080
>> disp(c)
0.27080
>> randn()
ans = 0.50997
>> randn()
ans = 0.31921
>> randn()
ans = -0.34053
>>
02. Assigning value to variables
>> a = 3
a = 3
>> b = a
b = 3
>> a = pi
a = 3.1416
>> s = 'Product Code'
s = Product Code
>> st = 'Product"
error: unterminated string constant
parse error:
syntax error
>>> st = 'Product"
^
>> st = "Product"
st = Product
>> a = rand()
a = 0.41793
>> a = randn()
a = -0.12372
>>
03. Introducing mathematical operators
- Math operators in Octave
-
+
, addition (e.g. 1 + 3 = 4) -
-
, subtraction (e.g. 3 - 1 = 2) -
*
, multiplication (e.g. 3 * 6 = 18) -
/
, division (e.g. 6 / 3 = 2) -
^
or**
, exponentiation求幂
(6 ^ 3 = 216) -
mod(x, y)
, modular模的
or reminder division (e.g. mod(5, 2) = 1)
-
- Logical operators in Octave
-
==
, is equal to (e.g. 5 == 5 is TRUE, 5 == 4 is FALSE) -
~=
or!=
, not equal to (e.g. 4 != 5 is TRUE) -
&&
, and (e.g. TRUE && TRUE is TRUE) -
||
, or (e.g. TRUE || FALSE is TRUE) -
xor(x, y)
, either x or y is TRUE, but not both (e.g. xor(TRUE, TRUE) is FALSE)
-
>> 3 + 5
ans = 8
>> 5 - 3
ans = 2
>> 5 * 3
ans = 15
>> 5 / 3
ans = 1.6667
>> 5 ^ 3
ans = 125
>> 5 ** 4
ans = 625
>> mod(24, 5)
ans = 4
>> a = 3
a = 3
>> b = 2
b = 2
>> a == b
ans = 0
>> b = 3
b = 3
>> a == b
ans = 1
>> a ~= b
ans = 0
>> true && false
ans = 0
>> true && true
ans = 1
>> 1 && 0
ans = 0
>> 1 && 1
ans = 1
>> 1 || 0
ans = 1
>> 0 || 0
ans = 0
>> 1 || 1
ans = 1
>> xor(1, 0)
ans = 1
>> xor(1, 1)
ans = 0
>>
04. Calculating values using built-in functions and variables
- Useful built-in functions
-
sqrt(x)
finds the square root of x -
nthroot(x)
finds the nth root of x (e.g. nthroot(27,3) returns 3) -
fix(x)
truncates截
a number and returns just the integer part -
ceil(x)
rounds a number up -
floor(x)
rounds a number down -
round(x)
rounds a number to the closest integer (.5 goes up) -
max(x)
finds the largest number in an input set -
min(x)
finds the smallest number in an input set -
factorial(x)
finds the factorial阶乘
of an input (e.g. 5! = 120) -
primes(x)
returns primes质数
up to x (e.g. primes (8) returns 2, 3, 5, 7) -
list_primes(x)
lists the first x primes
-
>> sqrt(16)
ans = 4
>> sqrt(15)
ans = 3.8730
>> nthroot(81, 4)
ans = 3
>> fix(3.5)
ans = 3
>> ceil(6.001)
ans = 7
>> floor(6.999)
ans = 6
>> round(4.49)
ans = 4
>> round(4.5)
ans = 5
>> v = [1, 2, 3, 4]
v =
1 2 3 4
>> max(v)
ans = 4
>> min(v)
ans = 1
>> factorial(5)
ans = 120
>> primes(23)
ans =
2 3 5 7 11 13 17 19 23
>> list_primes(23)
ans =
Columns 1 through 15:
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
Columns 16 through 23:
53 59 61 67 71 73 79 83
>>
05. Manipulating strings
- String assignments and concatenation
一系列相互关联的事物
Assign a string to a variable by enclosing it in either single or double quotes-
strcat(s1, s2...)
concatenates strings, which can be literals or variables, and removes whitespace at the end of a string -
cstrcat(s1, s2...)
concatenates strings, which can be literals or variables, and keeps whitespace at the end of a string
-
- Converting number to strings
-
num2str(x)
converts a number to a string -
num2str(x, p)
converts a number to a string, rounded top
digits
-
- String comparison
-
strcmp(s1, s2)
returns1
if strings are identical同一的
,0
otherwise -
strncmp(s1, s2, n)
returns1
if firstn
characters of strings are identical,0
otherwise -
strcmpi(s1, s2)
returns1
if the strings s1 and s2 are the same, ignoring case -
strncmpi(s1, s2, n)
returns1
if firstn
characters of strings are identical,0
otherwise, ignoring case
-
- String comparison (Trimming
修剪
and Processing Strings)-
deblank(s)
removes trailing拖尾的
whitespace from a string or array -
strtrim(s)
removes leading and trailing whitespace -
strtrunc(s, n)
truncates截
a string to length n
-
>> s1 = "Spring "
s1 = Spring
>> s2 = "catalog"
s2 = catalog
>> strcat(s1, s2)
ans = Springcatalog
>> cstrcat(s1, s2)
ans = Spring catalog
>> i = 551
i = 551
>> strcat(s2, i)
warning: range error for conversion to character value
ans = catalog
>> num1 = num2str(i)
num1 = 551
>> strcat(s1, num1)
ans = Spring551
>> strcmp(s1, s2)
ans = 0
>> s3 = deblank(s1)
s3 = Spring
>>
06. Performing conditional steps using if statements
- Creating a basic
if
statement
if (condition)
statement
endif
- File1:
sdata.m
% Created by Percy
% Script name is sdata
sales = 500
if (sales >= 500)
printf ("Sales target reached. \n");
endif
>> sdata
sales = 500
Sales target reached.
>>
- File2:
sdata.m
% Created by Percy
% Script name is sdata
sales = 400
if (sales >= 500)
printf ("Sales target reached. \n");
endif
>> sdata
sales = 400
>>
- Creating a basic
if...else
statement
if (condition)
statements
else
statements
endif
- File3:
sdata.m
% Created by Percy
% Script name is sdata
sales = 400
if (sales >= 500)
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
>> sdata
sales = 400
Sales target not reached.
>>
- File4:
sdata.m
% Created by Percy
% Script name is sdata
sales = 500
if (sales >= 500)
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
>> sdata
sales = 500
Sales target reached.
>>
- Creating a basic
if...elseif...else
statement
if (condition)
statements
elseif
staements
endif
- File5:
sdata.m
% Created by Percy
% Script name is sdata
sales = 500
if (sales >= 750)
printf ("Bonus target reached. \n");
elseif (sales = 500)
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
>> sdata
sales = 500
Sales target reached.
>>
- File6:
sdata.m
% Created by Percy
% Script name is sdata
sales = 400
if (sales >= 750)
printf ("Bonus target reached. \n");
elseif (sales = 500)
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
>> sdata
sales = 400
Sales target not reached.
>>
- File7:
sdata.m
% Created by Percy
% Script name is sdata
sales = 800
if (sales >= 750)
printf ("Bonus target reached. \n");
elseif (sales = 500)
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
>> sdata
sales = 800
Bonus target reached.
>>
3.Manipulating Matrices
01. Defining vector向量
and matrices矩阵
>> M = [1 2 3; 4 5 6]
M =
1 2 3
4 5 6
>> rv = [1 2 3]
rv =
1 2 3
>> cv = [1; 2; 3]
cv =
1
2
3
>>
02. Adding, subtracting, and multiplying matrices
- Subtraction requires matrices of the same dimensions
尺寸规格
- Multiplication requires matrices where the columns of the first matrix match the rows of the second matrix. The result is a matrix with the rows of the first matrix and the columns of the second.
- Matrix multiplication is not commutative
交换的
- order matters! - Adding, subtracting, multiplying, or dividing by a scalar value affects every element of the matrix.
>> M = [1 2 3; 4 5 6]
M =
1 2 3
4 5 6
>> N = [5 6; 7 8; 9 10]
N =
5 6
7 8
9 10
>> M * N
ans =
46 52
109 124
>> N * M
ans =
29 40 51
39 54 69
49 68 87
>> M * 4
ans =
4 8 12
16 20 24
>>
03. Generating useful matrices
>> ones(2, 3)
ans =
1 1 1
1 1 1
>> zeros(5, 4)
ans =
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
>> eye(3)
ans =
Diagonal Matrix
1 0 0
0 1 0
0 0 1
>> M = [1 2 3; 4 5 6; 7 8 9]
M =
1 2 3
4 5 6
7 8 9
>> M * eye(3)
ans =
1 2 3
4 5 6
7 8 9
>> v = [1: 0.1: 2]
v =
Columns 1 through 8:
1.0000 1.1000 1.2000 1.3000 1.4000 1.5000 1.6000 1.7000
Columns 9 through 11:
1.8000 1.9000 2.0000
>> W = rand(2, 3)
W =
0.89360 0.19536 0.34167
0.75238 0.21295 0.81458
>> randn(3, 4)
ans =
-0.076539 -0.236123 -0.630989 0.119407
-0.248545 -0.749690 -0.124957 0.616097
1.002778 -0.255473 -1.626574 -0.173041
>>
04. Transposing转置
and inverting逆
matrices
>> eye(2)
ans =
Diagonal Matrix
1 0
0 1
>> B = [1 2; 3 4]
B =
1 2
3 4
>> inv(B)
ans =
-2.00000 1.00000
1.50000 -0.50000
>> B * inv(B)
ans =
1.00000 0.00000
0.00000 1.00000
>> pinv(B)
ans =
-2.00000 1.00000
1.50000 -0.50000
>> A = [1 2 3; 4 5 6; 7 8 9]
A =
1 2 3
4 5 6
7 8 9
>>
05. Performing element-wise calculations
- Multiplying two matrices does not go element by element.
> A = [10 15; 20 25]
A =
10 15
20 25
>> A * 3
ans =
30 45
60 75
>> B = [4 8; 9 18]
B =
4 8
9 18
>> A * B
ans =
175 350
305 610
>> A .* B
ans =
40 120
180 450
>>
06. Referring to matrix rows and columns
>> v = [1: 0.1: 2]
v =
Columns 1 through 8:
1.0000 1.1000 1.2000 1.3000 1.4000 1.5000 1.6000 1.7000
Columns 9 through 11:
1.8000 1.9000 2.0000
>> v(7)
ans = 1.6000
>>v(7:9)
ans =
1.6000 1.7000 1.8000
>> A = [1 5; 8 9]
A =
1 5
8 9
>> A(2, 1)
ans = 8
>> A(2, :)
ans =
8 9
>> A(:, 1)
ans =
1
8
>>
4.Managing Executable Octave Programs
01. Sending output to the screen
- The following variable assignments and
printf()
command:
day = 2;
month = "August";
printf ("Signature validated on %s %d.\n Thank you!\n", month, day);
- Produce this output:
Signature validated on August 2.
Thank you!
sprintf()
uses the same conventions协议
, but sends the output to a sring variable- Helpful Codes for
printf()
andsprintf()
-
%i
prints an integer as a decimal number -
%u
prints an integer as an unsigned decimal number -
%f
prints a floating-point number in normal(fixed-point) notation -
%s
prints a string -
%%
prints a "%" character -
\n
prints a line feed character
-
>> day = 2
day = 2
>> month = "August"
month = August
>> printf ("Signature validated on %s %d.\n Thank you!\n", month, day)
Signature validated on August 2.
Thank you!
>> s = sprint("%s %d", month, day)
s = August 2
>> disp(s)
August 2
>>
02. Sending output to a file
- Assign the data to a variable, such as A
- Type a command such as
save datafile.mat A
- Can also use options
-
-ascii
writes the data without header information -
-append
appends data instead of overwriting, as long as you assign the data to a different variable name -
-mat7-binary
is MatLab version 7's binary format
-
- To write data to a comma-separated value file, use this command:
csvwrite("filename", X)
- File is saved to the directory with the Octave executable
>> a = [1 2; 3 4; 5 6]
a =
1 2
3 4
5 6
>> save -ascii datafile.mat A
>> csvwrite("csvdata.mat", A)
>>
03. Using data stored in a external file
- To assign the data to a variable, such as C, type a command such as
C = load("datafile.mat")
- To read data from a comma-separated value file, use this command:
csvread("filename")
- Octave looks in the directory with the Octave executable
>> C = load("datafile.mat")
C =
1 2
3 4
5 6
>> D = csvread("csvdata.mat")
D =
1 2
3 4
5 6
>>
04. Defining a function
- File:
displaypi.m
% create a file named displaypi.m
function displaypi
disp(pi);
endfunction
- Output
>> displaypi
3.1416
>>
- File:
timespi.m
% create a file named timespi.m
function timespi(x)
disp(x * pi);
endfunction
- Output
>> timespi(10)
31.416
>> timespi(8)
25.133
>>
- File:
cubed.m
% create a file named cubed.m
function retval = cubed(x)
retval = x ^ 3
endfunction
- Output
>> a = cubed(5)
retval = 125
a = 125
>>
05. Creating a executable script
- File:
firstscript.m
% Percy, July 1, 2018
a = 3;
disp(a * 3)
- Output
>> firstscript
9
>>
06. Adding comments to an Octave program
- Lines that start with a
%
or#
are comments - Can add a
%
on a line after the command; everything after it is a comment - Some good uses for comments are to indicate:
- The start of a script file so Octave doesn't confuse it for a function file
- When the file was created and by whom
- What type of data a file, function, or subroutine
子程序
expects - Whether the file depends on other files
- What subroutines do and how they do it
- File:
comments.m
# Created July 1, 2018 by Percy
sales = 800
% $750 is new daily target
if (sales >= 750);
printf ("Bonus target reached. \n");
elseif (sales = 500); % Formerly top bonus target amount.
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
07. Debugging your Octave code
- File:
debugging.m
% Testing if statements
sales = 800;
if (sales >= 500);
printf ("Bonus target reached. \n");
elseif (sales >= 750);
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
- Output
>> debugging
Bonus target reached.
>>
- File:
debugging.m
(fixed)
% Testing if statements
sales = 600;
if (sales >= 750);
printf ("Bonus target reached. \n");
elseif (sales >= 500);
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
- Output
>> debugging
Sales target reached.
- File:
debugging.m
(pause
)
% Testing if statements
sales = 600;
printf ("Press Enter to continue.")
pause;
if (sales >= 750);
printf ("Bonus target reached. \n");
elseif (sales >= 500);
printf ("Sales target reached. \n");
else
printf ("Sales target not reached. \n");
endif
- Output
>> debugging
Sales = 600
Press Enter to continue.
Sales target reached.
>>
5.Plotting Data
01. Creating a simple plot
- Code:
plot
>> X = -5:0.1:5
% there will be 101 results
>>plot(X, sin(X))
>>plot(X, cos(X))
>>
- Output:
sin(x)
- Output:
cos(x)
02. Summarizing data using a histogram柱状图
- Code:
hist
>> X = [1, 3, 7, 14, 15, 16, 14]
X =
1 3 7 14 15 16 14
>> hist(X)
>> hist(X, 3)
>>
- Output:
hist(x)
- Output:
hist(x, 3)
03. Creating a scatter分散
plot
- Code:
scatter
>> X = [1, 3, 5, 7, 9]
X =
1 3 5 7 9
>> Y = [15, 4, 18, 3, 9]
Y =
15 4 18 3 9
>> scatter(X, Y)
>> scatter(X, Y, "red")
>> scatter(X, Y, "red", "filled")
>>
- Output:
scatter(x, y)
- Output:
scatter(x, y, "red")
- Output:
scatter(x, y, "red", "filled")
6.Conclusion
Further Resources
- sourceforge.net and search for Octave
- The Manga Guide to Linear Algebra, from No Starch Press
- Data Science for Business, from O'Reilly Media