octave tutorial 2
Tags: octave
Computing on Data
- matrix multiply
a = [1 2; 3 4; 5 6] a = 1 2 3 4 5 6 b = [11 22; 33 44; 55 66] b = 11 22 33 44 55 66 c = [1 1; 2 2] c = 1 1 2 2 a * c >> ans = 5 5 11 11 17 17 % 單乘一個 (times element y only) a .* b ans = 11 44 99 176 275 396 % .(times element y only) a .^2 ans = 1 4 9 16 25 36 v = [1; 2; 3] v = 1 2 3 1 ./ v ans = 1.00000 0.50000 0.33333 - log
v = [1; 2; 3] v = 1 2 3 log(v) ans = 0.00000 0.69315 1.09861 - exp
exp(v) ans = 2.7183 7.3891 20.0855 - transpose
A = [1 2; 3 4; 5 6] A = 1 2 3 4 5 6 A' ans = 1 3 5 2 4 6 - max
a = [1 15 2 0.5] a = 1.00000 15.00000 2.00000 0.50000 max(a) 15 A = [1 2; 3 4; 5 6]; max(A) ans = 5 6 a < 3 ans = 1 0 1 1 find(a< 3) ans = 1 3 4 - magic
% A magic square is an arrangement of the integers '1:n^2' such that the row sums, column sums, and diagonal sums are all equal to the same value. A = magic(3) A = 8 1 6 3 5 7 4 9 2 A = magic(9) A = 47 58 69 80 1 12 23 34 45 57 68 79 9 11 22 33 44 46 67 78 8 10 21 32 43 54 56 77 7 18 20 31 42 53 55 66 6 17 19 30 41 52 63 65 76 16 27 29 40 51 62 64 75 5 26 28 39 50 61 72 74 4 15 36 38 49 60 71 73 3 14 25 37 48 59 70 81 2 13 24 35 sum(A, 1) ans = 369 369 369 369 369 369 369 369 369 sum(A, 2) ans = 369 369 369 369 369 369 369 369 369 - sum
- prod
- floor
-
ceil
- flipud
flipud(eye(9)) ans = Permutation Matrix 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 - pinv
A = magic(3) A = 8 1 6 3 5 7 4 9 2 pinv(A) ans = 0.147222 -0.144444 0.063889 -0.061111 0.022222 0.105556 -0.019444 0.188889 -0.102778 temp = pinv(A); temp* A ans = 1.00000 0.00000 -0.00000 -0.00000 1.00000 0.00000 0.00000 0.00000 1.00000
Plotting Data
- plot
t = [0 : 0.01 : 0.98] y1 = sin(2*pi*4*t) plot(t, y1) y2 = cos(2*pi*4*t) plot(t, y2) - plot in the same plot
t = [0 : 0.01 : 0.98] y1 = sin(2*pi*4*t) y2 = cos(2*pi*4*t) plot(t, y1) hold on; plot(t, y2, 'r') % 紅色的線 xlabel('time') ylabel('value') legend('sin', 'cos') title('my plot') - 出圖
print -dpng 'xxx.png' - close
- close plot
- figure
figure(1): plot(t, y1); figure(2): plot(t, y2) - subplot
subplot(1, 2, 1); % Divides plot a 1 x2 grid, access first element plot(t,y1) subplot(1, 2, 2) plot(t,y2) - imagesc % 水水的格子
A = magic(9); imagesc(A) % colorbar imagesc(A), colorbar, colormap gray;