Tutorial 1 SEG7550 Introduction to MATLAB

1. Tutorial 1 SEG7550Introduction to MATLAB 18th, SEP. 2009

2. Announcement • If you are from other departments other than SEEM, leave your student ID, name and department to me before you leave. A temporary account will be created for you.

3. Access MATLAB outside campus • 1 Department VPN service currently is only available to SEEM/AECT Staff, gds and MSc only . • 2 Idle timeout of 4 hours • 3 First set up a vpn: http://www.cuhk.edu.hk/itsc/network/vpn/index.html • 4 Running X Applications (UNIX) remotely from MS Windows with VPN https://www-sl.se.cuhk.edu.hk/seem/index.php/Computer_Facilities:External_Access_Route#Running_X_Applications_.28UNIX.29_remotely_from_MS_Windows_with_VPN

4. Introduction to MATLAB • Current version in lab: MATLAB 7.9.0 (R2009b) • Help: F1 • In most cases, we will need to read function help.

5. Function help

6. Programs • Usually long programs will be written in m file. (File->new->blank m-file) • To run the program, press (save and run), or F5.

7. Initial a matrix • Ones: Create array of all ones Syntax:Y = ones(n); Y = ones(m,n); • Zeros: Create array of all zeros Syntax:Y = zeros(n); Y = zeros(m,n);

8. Vector Functions • Addition: A = [1 2 3] B = [6 4 7] A + B = ?

9. Vector Functions • In Matlab A = [1 2 3]; B = [6 4 7]; A + B • ans = 7 6 10

10. Vector Functions • Substraction • A = [11 2 13] B = [7 4 7] A -B = ?

11. Vector Functions • In Matlab A = [11 2 13]; B = [7 4 7]; A - B • ans = 4 -2 6

12. Vector Functions • Multiplication • In matrix calculation, there are two kinds of multiplication, element by element and matrix multiplication. • Please note that the multiplication of vector must match their size. For example, the size of A and B are m x n and k x j vector respectively. Then m must be equal to k • For element by element multiplication, two matrix must have same size.

13. Vector Functions • A = [1 2 3] B = [2 2 3]' A * B' = ? and A' * B = ?

14. Vector Functions • In Matlab A = [1 2 3]; B = [2 2 3]; A * B Error using ==> * Inner matrix dimensions must agree • A * B' ans = 15 • A' * B ans = 2 2 3 4 4 6 6 6 9

15. Vector Functions A = [1 2 3] B = [2 3 1] we want aij * bij, how?

16. Vector Functions • In Matlab A = [1 2 3]; B = [2 3 1]; A .*B ans = 2 6 3

17. Vector Functions • Division element by element (i.e. aij / bij): “./” • A = [ 4 6 10] B = [2 3 5] aij ./ bij = ?

18. In Matlab A = [4 6 10]; B = [2 3 5]; A./B ans = 2 2 2

20. If • if expression, statements, end • If can be used with else, elseif to deal with complicated cases • if expression1 statements1 elseif expression2 statements2 else statements3 end

21. An exercise • Could you use Matlab to implement the following logic? • Case OP_CP > 0 and OP_LO > 0 and CP_HI <= 0 : A = 1 Case OP_CP = 0 and OP_LO > 0 and CP_HI < 0 : A = 2 Case OP_CP = 0 and OP_LO = 0 and CP_HI < 0 : A =3 Otherwise, A=4

22. Answer • Matlab Code: if op_cp > 0 & op_lo >= 0 & cp_hi <= 0 A = 1; elseif op_cp == 0 & op_lo > 0 & cp_hi < 0 A = 2; elseif op_cp = 0 & op_lo = 0 & cp_hi < 0 A = 3; else A = 4; end

23. FOR • Repeat statements a specific number of times. • for x=initval:endval, statements, end • Example: Assign 1,2,3,4,5 ... 10 to A(1), A(2), A(3), A(4), A(5), ... A(10) use if.

24. A=zeros(10,1); for j=1:10, A(j) = j; end

25. while • Repeatedly execute statements while condition is true. • Syntax: while expression, statements, end • Example Assign 1,2,3,4,5 ... 10 to A(1), A(2), A(3), A(4), A(5), ... A(10) use while.

26. A=zeros(10,1); j=1; while j<11 A(j) = j; j=j+1; end

27. Example: Manipulation of the specific row of matrix or vectorsA = [1 2 3 6 1 4 7 9 2 ] • Subtract the 2nd row from 1st row of 3 x 3 matrix

28. In Matlab A = [ 1, 2, 3;6,1,4;7, 9, 2; ] A =1 2 3 6 1 4 7 9 2 for j=1:3, A(2,j) = A(2,j) - A(3,j); end A ans = 1 2 3 -1 -8 2 7 9 2