常見命令及函數(shù)
disp() % display
disp(sprintf('2 decimals: %.2f', pi)) % format output
format long % set ‘long’ as default variable format
format short
A = [1 2; 3 4; 5 6] % new a matrix
v = 1:0.1:2 % new a row vector from 1 to 2 with a interval of 0.1
k*ones(m, n) % new a m by n matrix with all elements equaling to k
zeros(m, n)
rand(m,n) % new a m by n matrix with random elements drawn from the uniform distribution between 0 and 1
randn() % all the values drawn from a Gaussian distribution with mean 0 and variance or deviation equal to 1
w = -6 + sqrt(10)*(randn(1,10000)) % mean is -6, standard deviation is square root of 10
hist(w, 50) % draw a histogram of 50 bins with w as the dataset
eye(4) % new a 4 by 4 identity matrix
help % how to use a command or a function
size(A) % the size of a matrix, output another matrix
size(A, 1) or size (A, 2)
length(v) % the size of the longest dimension
load('priceY.dat')
load featuresX.dat % load data file
who % all the variables that Octave has in memory currently
whos % that gives you the detailed view
clear % clear all the variables in memory
v = priceY(1:10) % get elements from 1 to 10
save hello.mat v % save data from variable v to the file named hello.mat
save filename variable -ascii (or -text et cetera)
A(2,3)
A(2,:) % ':' refer to a range
A(m) % one parameter, m can be a number or a range
A(m, n) % two params, choose elements by row and column
Computing on data
C = A * B
% element wise functions
A .* B % element-wise multiplications of two matrices
A .^ 2
1 ./ A
log(v)
exp(v)
abs(v)
-v % minus v
A' % the transpose of A
[value, index] = max(a) % when a is a matrix, max() will be executed in every column
find(a < 3) % find all the elements that are less than 3
magic(m) % m by m matrix that complies with sudoku
[r, c] = find(A >= 7) % row r, column c
i = find(A >= 7) % a column vector of indexes
sum(a)
prod(a)
floor(a)
ceil(a)
max(A, B, 1(or 2)) % matrix A and B, 1: get by columns, 2: get by rows
max(A(:))
max(max(A))
sum(A, 1(or 2)) % sum by columns(1), or rows(2)
sum(sum(A .* eye(9))) % sum of the diagonal elements
flipud() % flip updown matrix
pinv(A) % the inverse of A
Plotting data
t = [0:0.01:0.98];
y1 = sin(2*pi*t);
plot(t, y1);
hold on;
plot(t, y2);
xlabel('time');
ylabel('value');
legend('sin', 'cos')
title('my plot')
axis([0 4 -1 10]) % set axis range
print -dpng 'myplot.png' % save image
close % close current figure
figure(1); plot(t, y1)
figure(2); plot(t, y2)
subplot(1,2,1);
clf % clear current figure
imagesc(magic(15))
colorbar
colormap gray % background image
Control statements
% if
c = 1;
if c == 1,
disp('The value is one');
elseif c == 2,
disp('The value is two');
else
disp('We don\'t know the value')
end % end if
% for
for i = 1:10,
disp(i);
end;
% while
i = 1;
while i<5,
disp(i);
++i;
end;
Function
create a file named by ***.m in the current path
or you have to addpath('absolute/relative path')
