Octave(MATLAB)
Octave笔记
- 变量
- 矩阵操作
- 常用函数
- 决策
- 绘图
MATLAB w3c
MATLAB_台大郭彦甫
变量
变量赋值
a = 1;
A = 2;
a
A
a = 1
A = 2
数值型
class(int8(1))
class([1 2 3])
ans = int8
ans = double
字符串
class('Hello World!')
ans = char
逻辑型
class(true)
ans = logical
结构体
student.name = 'John Doe';
student.id = 301073268;
student.grade = [100 75 73;...
95 91 85;...
100 98 72];
class(student)
student
ans = struct
student =
scalar structure containing the fields:
name = John Doe
id = 301073268
grade =
100 75 73
95 91 85
100 98 72
元胞
A{1, 1} = [1 4 3; 0 5 8; 7 2 9];
A{1, 2} = 'Anne Smith';
A{2, 1} = 3 + 7i;
A{2, 2} = -pi:pi:pi;
class(A)
A
error: scalar cannot be indexed with {
error: scalar cannot be indexed with {
error: scalar cannot be indexed with {
error: scalar cannot be indexed with {
ans = double
A = 2
矩阵操作
创建向量
vr = [1 2 3] % 行向量
vc = [1; 2; 3] % 列向量
vr =
1 2 3
vc =
1
2
3
创建矩阵
M = [1 2 3; 4 5 6; 7 8 9]
M =
1 2 3
4 5 6
7 8 9
矩阵索引
M = [1 2 3; 4 5 6; 7 8 9]
M(8) % 索引从1开始，第8个元素
M(:, 2) % 第2列
M(1:2, [1 3]) % 1,2行1,3列
M =
1 2 3
4 5 6
7 8 9
ans = 6
ans =
2
5
8
ans =
1 3
4 6
特殊矩阵
a = linspace(1, 10, 3) % 间隔数组
b = eye(2) % 单位矩阵
c = zeros(2) % 零矩阵
d = ones(2) % 一矩阵
e = diag([1 2 3]) % 对角矩阵
f = rand(2) % U(0,1)
g = randn(2) % N(0,1)
a =
1.0000 5.5000 10.0000
b =
Diagonal Matrix
1 0
0 1
c =
0 0
0 0
d =
1 1
1 1
e =
Diagonal Matrix
1 0 0
0 2 0
0 0 3
f =
0.54306 0.91400
0.27150 0.13563
g =
0.31237 -1.02912
-0.42424 -0.58838
矩阵运算
M1 = magic(3);
M2 = inv(M1);
M1 * M2 % 矩阵乘法
M1 .* M2 % 矩阵点乘
ans =
1.00000 0.00000 -0.00000
-0.00000 1.00000 0.00000
0.00000 0.00000 1.00000
ans =
1.177778 -0.144444 0.383333
-0.183333 0.111111 0.738889
-0.077778 1.700000 -0.205556
矩阵与向量间运算
v = [1; 2; 3]
M = ones(3)
M + v
v =
1
2
3
M =
1 1 1
1 1 1
1 1 1
ans =
2 2 2
3 3 3
4 4 4
矩阵合并
M1 = magic(3);
M2 = M1';
M3 = [M1, M2] % 水平合并
M4 = [M1; M2] % 竖直合并
M3 =
8 1 6 8 3 4
3 5 7 1 5 9
4 9 2 6 7 2
M4 =
8 1 6
3 5 7
4 9 2
8 3 4
1 5 9
6 7 2
***操作符
a = 1:3
b = 1:2:5
c = 9:-1:7
a =
1 2 3
b =
1 3 5
c =
9 8 7
常用函数
自定义函数 f u n c t i o n [ o u t 1 , o u t 2 , . . . , o u t M ] = f u n N a m e ( i n 1 , i n 2 , i n 3 , . . . , i n N ) function [out1,out2, ..., outM] = funName(in1,in2,in3, ..., inN) function [out1,out2,...,outM] = funName(in1,in2,in3,...,inN)
最大值、最小值
M = magic(3)
max(M) % 最大值
min(M) % 最小值
M =
8 1 6
3 5 7
4 9 2
ans =
8 9 7
ans =
3 1 2
平均值、标准差
M = magic(3)
mean(M) % 平均值
std(M) % 标准差
M =
8 1 6
3 5 7
4 9 2
ans =
5 5 5
ans =
2.6458 4.0000 2.6458
求和
M = magic(3)
sum(M) % 求和
M =
8 1 6
3 5 7
4 9 2
ans =
15 15 15
排序
M = magic(3)
sort(M) % 排序
M =
8 1 6
3 5 7
4 9 2
ans =
3 1 2
4 5 6
8 9 7
维度
M = ones(2, 3)
size(M)
M =
1 1 1
1 1 1
ans =
2 3
转置、逆、行列式、秩、最简形
M = magic(3)
A = M'
B = inv(M)
C = det(M)
D = rank(M)
E = rref(M)
M =
8 1 6
3 5 7
4 9 2
A =
8 3 4
1 5 9
6 7 2
B =
0.147222 -0.144444 0.063889
-0.061111 0.022222 0.105556
-0.019444 0.188889 -0.102778
C = -360
D = 3
E =
1 0 0
0 1 0
0 0 1
长度
s = 'Hello World!'
length(s)
v = [1 2 3]
length(v)
M = zeros(2, 3)
length(M)
s = Hello World!
ans = 12
v =
1 2 3
ans = 3
M =
0 0 0
0 0 0
ans = 3
决策
逻辑判断
1 == 2
1 ~= 2
1 < 2
true && false
true || false
~false
ans = 0
ans = 1
ans = 1
ans = 0
ans = 1
ans = 1
if 语句
a = 30;
if a == 10
disp('Value of a is 10');
elseif a == 20 || a == 30
disp('Value of a is 20 or 30');
else
disp('None of the values are matching');
end
Value of a is 20 or 30
switch 语句
grade = 'B';
switch(grade)
case 'A'
disp('Excellent!');
case 'B'
disp('Well done');
case 'C'
disp('Well done');
case 'D'
disp('You passed');
case 'F'
disp('Better try again');
otherwise
disp('Invalid grade');
end
Well done
while 语句
a = 10;
while a < 20
fprintf('value of a: %d \n', a);
a = a + 1;
end
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19
for 语句
for a = 10:20
fprintf('value of a: %d \n', a);
end
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19
value of a: 20
绘图
x = linspace(-pi, pi, 100);
y1 = sin(x);
y2 = cos(x);
hold on % 一张图中显示多条线
plot(x, y1, 'r');
plot(x, y2, 'b');
legend('sin(x)', 'cos(x)') % 标签
title('Graph') % 标题
xlabel('x') % 横坐标名称
ylabel('y') % 纵坐标名称
axis([-pi pi -1 1]) % 坐标轴范围
hold off
