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Unformatted text preview: 14:440:127 Introduction to Computers for Engineers Lecture 8 LEASE TAKE LECTURE 8 NOTES PLEASE TAKE LECTURE 8 NOTES AS YOU ENTER THE ROOM! Lecturer: Blase E. Ur Recitation Instructor: Bo Jin Recitation Instructor: Cyrus Gerami Recitation Instructor: Vishnu Vijayakumar Recitation Instructor: Wen Yueh 14:440:127 Lecture 8 Efficiency 1) Loops are bad 2) Preallocating memory is good Rutgers University School of Engineering 14:440:127 Lecture 8 Efficiency 1) Loops are bad 1) tic (starts a timer) 2) toc (stops a timer) Rutgers University School of Engineering 14:440:127 Lecture 8 Efficiency Preallocate memory tic for z = 1:10000 x(z) = 5; end toc % this took 0.18 seconds Rutgers University School of Engineering tic V = zeros(1,10000); % preallocating! for j = 1:10000 V(j) = 5; end toc % this took 0.0001 seconds 14:440:127 Lecture 8 Efficiency 1) Better: use builtin functions % Use builtin functions tic x = 5*ones(1,10000); Rutgers University School of Engineering x = 5*ones(1,10000); toc % 0.000059 seconds 14:440:127 Lecture 8 Animation 1) Make a loop 2) Each time you go through the loop, change something 3) Pause each time you go through the loop 4) Have a constant axis Rutgers University School of Engineering 14:440:127 Lecture 8 Animation % X floating through space for t=0:0.1:20 % choose a small interval x=t*cos(t); y=5*sin(t); pause(0.05) % can come anywhere in the loop Rutgers University School of Engineering pause(0.05) % can come anywhere in the loop plot(x,y,'X') axis([20 20 5 5]) % must follow plot end 14:440:127 Lecture 8 Animation % X floating through space, precomputed t = 0:0.1:20; x=t.*cos(t); % don't forget dot operations y=5*sin(t); for j = 1:length(x) Rutgers University School of Engineering for j = 1:length(x) pause(0.05) % can come anywhere in the loop plot(x(j),y(j),'X') axis([min(x) max(x) min(y) max(y)]) end 14:440:127 Lecture 8 Animation % X floating through space, leaving a trail t = 0:0.1:20; x=t.*cos(t); % don't forget dot operationsx=t....
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This note was uploaded on 01/11/2010 for the course 440 127 taught by Professor Blase during the Fall '09 term at Rutgers.
 Fall '09
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