Transcript Matlab Class 2

Matlab Class 2
Xiaotao Su, Ph.D.
Visual Psychophysicist & IT Group Leader
Rutgers Center for Cognitive Science (RuCCS)
RuCCS
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
h
e
l
l
o
w
o
r
(1) (2) (3) (4) (5) (6) (7) (8) (9)
35
26.3
11
4
(1)
(2)
(3)
(4)
l
d
(10) (11)
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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
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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
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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(num1num2)]);
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boolean expressions
• Boolean expressions either return
1 for true
or
0 for false
• Possible operators:
==
>
>=
<
<=
&
equals
greater
than
greater less than greater and
than or
than or
equal to
equal to
|
or
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•
•
•
•
•
•
•
1==1
(1 + 1)==2
(5 + 5) < 10
(5 + 5) <=10
(1 == 1) & (2==3)
(1 == 1) | (2==3)
5 + (5 < 10)
Note: Put operations inside
parenthesis so they are
preformed first.
==
>
>=
<
<=
&
equals
greater
than
greater less than greater and
than or
than or
equal to
equal to
|
or
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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
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Back to math.m
if ( (round(num1)==num1) & (round(num2)==num2) )
disp('num1 and num2 are integers')
end
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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
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Task 1
• Have math.m tell me which number is larger then the other
“the biggest number is …”
==
>
>=
<
<=
&
equals
greater
than
greater less than greater and
than or
than or
equal to
equal to
|
or
RuCCS
Screen drawing and psychtoolbox
Origin
Screen Geometry
X ----------- Positive ->
Y
Positive
Coordinates are
measured in
pixels.
Max X and Y
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How you typically work with the psychtoolbox
Back Buffer
(invisible)
Front Buffer
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How you typically work with the psychtoolbox
Step 1: Draw
Shape to the
back buffer
Front Buffer
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How you typically work with the psychtoolbox
Step 2:
Flip the back buffer
to the front buffer
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How you typically work with the psychtoolbox
Back Buffer is automatically cleared
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How you typically work with the psychtoolbox
Now you can
continue with
your next
frame of
animation
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How you typically work with the psychtoolbox
Flip the back buffer
to the front buffer
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How you typically work with the psychtoolbox
Back Buffer is automatically cleared
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Set up program draw_stuff
% draw_stuff.m
%
% Draws stuff on the screen
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Initialize the main window
% draw_stuff.m
%
% Draws stuff on the screen
clear all;
which_screen=0;
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Set up program draw_stuff
% draw_stuff.m
%
% Draws stuff on the screen
0
clear all;
which_screen=0;
[window_ptr, screen_dimensions]
=Screen(0,'OpenWindow', [0, 0, 0]);
0 is main screen
(allows for multiple
monitors)
Command issued
to the
psychtoolbox
Screen function
Vector specifying
Screen color
[red, green, blue]
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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]);
x1= 0
y1 = 0
Vector [x1, y1, x2, y2]
Which could be:
[0, 0, 800, 600]
For an 800 X 600 display
x2= 800 y2 = 600
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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
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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
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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;
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Tic and toc
• tic starts a timer
• toc tells you the number of seconds since when you ran toc
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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
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While program
tic
loops = 0;
while(toc<5)
loops = loops+1;
disp(['number of loops = ', num2str(loops)]);
disp(['number of seconds = ', num2str(toc)]);
end
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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
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);
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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
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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]