Character Vectors And Numeric Vectors

1. Matlab Class 2Xiaotao Su, Ph.D.Visual Psychophysicist & IT Group LeaderRutgers Center for Cognitive Science (RuCCS)

2. Character Vectors And Numeric Vectors • 'hello world' is referred to as a character string or a character vector • [35, 26.3, 11, 4] is a numeric vector • These are the two main data types in matlab

3. Character Vectors (aka Strings) And Numeric Vectors • How to convert between these two data types? What if I have a string, '39.5' and I want to add to it? • num2str & str2num • str2num('39.5') + 5 • ['hello w', 'orld'] • a = [3, 9]; • b = [12.6, 8]; • [a, b] • c = ['1', num2str(39.5)] • str2num(c) + 200

4. Taking inputs • Create a new program called math.m % math.m % % Carries out a series of calculations on two % numbers % % written by Your Name July 2010

5. clear all; %take inputs num1=input('what is the first number?'); num2=input('what is the second number?'); %show calculations disp([num2str(num1), '+', num2str(num2), '=', num2str(num1+num2)]); disp([num2str(num1), '-', num2str(num2), '=', num2str(num1-num2)]);

6. boolean expressions • Boolean expressions either return1 for trueor 0 for false • Possible operators:

7. Note: Put operations inside parenthesis so they are preformed first. • 1==1 • (1 + 1)==2 • (5 + 5) < 10 • (5 + 5) <=10 • (1 == 1) & (2==3) • (1 == 1) | (2==3) • 5 + (5 < 10)

8. Conditionals (if statements) if(Boolean Expression) do something end you can also do this: if(boolean expression) do something else do something else end or this: if(boolean expression) do something elseif(boolean expr2) do something else end

9. Back to math.m if ( (round(num1)==num1) & (round(num2)==num2) ) disp('num1 and num2 are integers') end

10. if ( (round(num1)==num1) & (round(num2)==num2) ) disp('num1 and num2 are integers') elseif(round(num1)==num1) disp('only num1 is an integer') elseif(round(num2)==num2) disp('only num2 is an integer') else disp('neither number is an integer') end

11. Task 1 • Have math.m tell me which number is larger then the other “the biggest number is …”

12. Screen drawing and psychtoolbox Screen Geometry Origin Coordinates are measured in pixels. X ----------- Positive -> Y Positive Max X and Y

13. How you typically work with the psychtoolbox Back Buffer (invisible) Front Buffer

14. How you typically work with the psychtoolbox Step 1: Draw Shape to the back buffer Front Buffer

15. How you typically work with the psychtoolbox Step 2: Flip the back buffer to the front buffer

16. How you typically work with the psychtoolbox Back Buffer is automatically cleared

17. How you typically work with the psychtoolbox Now you can continue with your next frame of animation

18. How you typically work with the psychtoolbox Flip the back buffer to the front buffer

19. How you typically work with the psychtoolbox Back Buffer is automatically cleared

20. Set up program draw_stuff % draw_stuff.m % % Draws stuff on the screen

21. Initialize the main window % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0;

22. Set up program draw_stuff % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0; [window_ptr, screen_dimensions] =Screen(0,'OpenWindow', [0, 0, 0]); 0 Vector specifying Screen color Command issued to the psychtoolbox Screen function 0 is main screen (allows for multiple monitors) [red, green, blue]

23. Set up program draw_stuff % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0; [window_ptr, screen_dimensions]=Screen(0,'OpenWindow', [0, 0, 0]); Vector [x1, y1, x2, y2] Which could be: [0, 0, 800, 600] For an 800 X 600 display x1= 0 y1 = 0 x2= 800 y2 = 600

24. Draw shape in back buffer % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0; [window_ptr, screen_dimensions]=Screen(0,'OpenWindow', [0, 0, 0]); shape_dimensions = screen_dimensions/2; Screen(window_ptr, 'FillRect', [0,0,255], shape_dimensions); X1, Y1 Front buffer X2, Y2 Back buffer

25. Flip the back buffer to the front buffer % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0; [window_ptr, screen_dimensions]=Screen(0,'OpenWindow', [0, 0, 0]); shape_dimensions = screen_dimensions/2; Screen(window_ptr, 'FillRect', [0,0,255], shape_dimensions); %Flip the buffers Screen(window_ptr,'Flip'); Front buffer Back buffer

26. Clear screen <<<<snip>>>> clear all; which_screen=0; [window_ptr, screen_dimensions]=Screen(0,'OpenWindow', [0, 0, 0]); shape_dimensions = screen_dimensions/2; Screen(window_pointer, 'FillRect', [0,0,255], shape_dimensions); %Copy to main window Screen(window,'Flip'); %leave the image up for 5 seconds WaitSecs(5); %Clear screen and return control to matlab clear screen;

27. Tic and toc • tic starts a timer • toc tells you the number of seconds since when you ran toc

28. While loop • while is a type of loop that runs while a condition is true while(boolean statement) %do something many times end %you would stop repeating the loop when the %boolean statement is false OR if you use %break

29. While program tic loops = 0; while(toc<5) loops = loops+1; disp(['number of loops = ', num2str(loops)]); disp(['number of seconds = ', num2str(toc)]); end

30. While program stopping after 10 loops tic loops = 0; while(toc<5) loops = loops+1; disp(['number of loops = ', num2str(loops)]); disp(['number of seconds = ', num2str(toc)]); if(loops>=10) break; end end

31. Making a movie % draw_stuff.m % % Draws stuff on the screen clear all; which_screen=0; [window_ptr, screen_dimensions] …=Screen(0,'OpenWindow', [0, 0, 0]); shape_dimensions = screen_dimensions/2; Screen(window_pointer, 'FillRect', … [0,0,255], shape_dimensions);

32. Task 2 Make the rectangle move to the bottom of the screen at 5 pixels per frame, then move right when it hits the bottom. When it hits the right, the program ends Hint: shape_dimensions(1) is x1, (2) is y1, (3) is x2, 4 is y2

33. Task 3 When the rectangle hits the bottom make it change colors to red Hint: color is a 3 number vector red is [255, 0, 0]