how can I compare the execution time of two different methods simultaneously in MatLab?
actually I used "tic-toc" but I'm not sure if I did it in a correct way or not.
this is how I do it:
clc;
clear all;
A=rand(10);
B=rand(50;
tID1=tic;
y1=function1(A,B);
t1=toc(tID1);
tID2=tic;
y2=function2(A,B);
t2=toc(tID2);
Use matlab's built in profiler for better understanding of your code's run-time bottlenecks.
profile clear; %// reset profiler's history
profile on; % start recording
y1 = function1( A, B ); % your code here...
y2 = function2( A, B );
profile off; % stop recording
profile viewer; % visualize the results.
Enjoy!
Yes. That is correct. You don't even need to define tID1 and tID2 the way you are using it. So you can also do:
clc;
clear all;
A=rand(10);
B=rand(50;
tic;
y1=function1(A,B);
t1=toc;
tic;
y2=function2(A,B);
t2=toc;
Related
I have a while loop inside of which I have to use a plot and a chasePlot function.
The problem is, it comes up with a new window figure each time the loop runs. I somehow want a single frame which can be updated rather than each time making a new window and figure for it.
Anybody knows how to prevent a new figure in each loop so that one figure is there and that keeps on updating.
Don't use 'figure' before the 'plot' command and the code will keep overwriting every time on the same figure. You can also use the 'drawnow limitrate' command for better visualization. See an example below:
clc; close all; clear all;
x = 0 :100 :1e5;
y = zeros(size(x));
for n = 1:numel(x)
y(n) = sin(x(n));
plot(x(1:n), y(1:n));
drawnow limitrate;
end
I want to create a frontend where the user can browse pictures forward by pressing Enter.
Pseudo-Code
hFig=figure
nFrames=5;
k=1;
while k < nFrames
u=signal(1*k,100*k,'data.wav'); % 100 length
subplot(2,2,1);
plot(u);
subplot(2,2,2);
plot(sin(u));
subplot(2,2,3);
plot(cos(u));
subplot(2,2,4);
plot(tan(u));
% not necessary but for heading of overal figure
fprintf('Press Enter for next slice\n');
str=sprintf('Slice %d', k);
mtit(hFig, str);
k=k+1;
keyboard
end
function u=signal(a,b,file)
[fs,smplrt]=audioread(file);
u=fs(a:b,1);
end
where
something is wrong in updating the data because pressing CMD+Enter increases k by one but does not update the data. Sometimes (rarely), the data is once the next iteration.
something is wrong with while's condition because k can be bigger than nFrames. keyboard just keep asking for more inputs.
My mistake earlier in Error-Checking
I had earlier a problem where the closure of the window lead to the crash of the application. I include this here because I mentioned a problem about it in the comment of one answer. I avoid the problem now by
hFig=figure;
n=5;
k=1;
while k<nFrames
% for the case, the user closes the window but starts new iteration
if(not(ishandle(hFig)))
hFig=figure;
end
...
end
which creates a new Figure if the earlier was closed by the user.
I tried unsuccessfully putting hFig=figure; inside the while loop's if clause earlier to avoid repetition in the code.
Please, let me know if you know why you cannot have the handle hFig in the while loop's if clause.
How can you loop subplots with updated outputs in Matlab?
To stop the script waiting for an input from the user you should use input instead of keyboard.
Actually keyboard makes your script entering in a debug mode. It stops the executino of the script as (like a breakpoint) allowing the user to, for example, check the value of a variable.
You can modify your scripr as follows (modification are at the end of your script, identified by "UPDATED SECTION):
hFig=figure
nFrames=5;
k=1;
while k < nFrames
u=signal(1*k,100*k,'handel.wav'); % 100 length
subplot(2,2,1);
plot(u);
subplot(2,2,2);
plot(sin(u));
subplot(2,2,3);
plot(cos(u));
subplot(2,2,4);
plot(tan(u));
% not necessary but for heading of overal figure
%
% UPDATED SECTION
%
% Use the string "Press Enter for next slice\n" as the prompt for the
% call to "input"
%
% fprintf('Press Enter for next slice\n');
% str=sprintf('Slice %f', k);
% Use %d instead of "%f" to print integer data
str=sprintf('Slice %d', k);
mtit(hFig, str);
k=k+1;
% Use "input" instead of "keyboard"
% keyboard
input('Press Enter for next slice\n')
end
Hope this helps.
Qapla'
First time post here. Pretty frustrated right now working on this assignment for class.
Basically, the idea is to use Euler's method to simulate and graph an equation of motion. The equation of motion is in the form of an ODE.
My professor has already put down some code for slightly similar system and would like us to derive the equation of motion using Lagrange. I believe that I have derived the EOM correctly, however I am running into problems on the Matlab side of things.
What's weird is that using a similar technique on another, seperate EOM, I have no issues. So I am unsure what I am doing wrong.
Here's the code for the part that is working correctly:
close all; clear all; clc;
% System parameters
w = 2*pi;
c = 0.02;
% Time vectors
dt = 1e-5;
t = 0:dt:4;
theta = zeros(size(t));
thetadot = zeros(size(t));
% Initial conditions
theta(1)=pi/2; %theta(0)
thetadot(1)=0; %thetadot(0)
for I = 1 : length(t)-1;
thetaddot = -c*thetadot(I)-w^2*sin(theta(I));
thetadot(I+1)=thetadot(I)+thetaddot*dt;
theta(I+1)=theta(I)+thetadot(I)*dt ;
end
figure(1);
plot(t,theta,'b');
xlabel('time(s)');
ylabel('theta');
title('Figure 1');
zoom on;
% Output the plot to a pdf file, and make it 6 inches by 4 inches
printFigureToPdf('fig1.pdf', [6,4],'in');
% Open the pdf for viewing
open fig1.pdf
Everything runs fine, except Matlab complains about the printFigureToPdf command.
Now, here is the code for the problem that I am having issues with.
close all; clear all; clc; clf
% System parameters
m=0.2;
g=9.81;
c=.2;
d=0.075;
L=0.001; %L is used for Gamma
B=0.001; %B is used for Beta
W=210*pi; %W is used for Omega
%Time vectors
dt = 1e-6; %Time Step
t=0:dt:10; %Range of times that simulation goes through
x=zeros(size(t));
xdot=zeros(size(t));
%Initialconditions
x(1)=0;%x(0)
xdot(1)=0; %xdot(0)
for I = 1 : length(t)-1;
xddot =-1/m*(c*xdot(I)-c*L*W*cos(W)+m*g-3*B*((d+x-L*W*sin(W*t)).^(-4)-(d-x-L*W*sin(W*t)).^(-4)));
xdot(I+1)=xdot(I)+xddot*dt;
x(I+1)=x(I)+xdot(I+1)*dt ;
end
figure(1);
plot(t,x,'b');
xlabel('time(s)');
ylabel('distance(m)');
title('Figure 2');
zoom on;
% Output the plot to a pdf file, and make it 6 inches by 4 inches
printFigureToPdf('fig1.pdf', [6,4],'in');
% Open the pdf for viewing
open fig1.pdf
With this code, I followed the same procedure and is giving an error on line 23: "In an assignment A(I) = B, the number of elements in B and I must be the same."
Like I said, I am confused because the other code worked okay, and this second set of code gives an error.
If anyone could give me a hand with this, I would greatly appreciate it.
Thanks in advance,
Dave
Edit: As suggested, I changed x(I+1)=x(I)+xdot(I+1)*dt to x(I+1)=x(I)+xdot(I)*dt. However, I am still getting an error for line 23: "In an assignment A(I) = B, the number of elements in B and I must be the same."
Line 23 is: xdot(I+1)=xdot(I)+xddot*dt;
So, I tried adjusting the code as suggested for the other line to xdot(I+1)=xdot(I)+xddot(I)*dt;
After making this change, Matlab gets stuck, I tried letting it run for a few minutes but won't execute. I ended up having to close and reopen the application.
The error In an assignment A(I) = B, the number of elements in B and I must be the same. is something you should understand because it may pop up frequently in Matlab if you are not careful.
In your case, you are trying to assign 1 element value xdot(I+1) with something which has more than 1 element xdot(I)+xddot*dt.
Indeed, if you step through the code line by line and observe your workspace, you will notice that xddot is not a scalar value as intended, but a full blown vector the size of t. This is because in the precedent line where you define xddot:
xddot =-1/m*(c*xdot(I)-c*L*W*cos(W)+m*g-3*B*((d+x-L*W*sin(W*t)).^(-4)-(d-x-L*W*sin(W*t)).^(-4)));
you still have many references to x (full vector) and t (full vector). You have to replace all these references to full vectors to only one index of them, i.e use x(I) and t(I). The line becomes:
xddot =-1/m*(c*xdot(I)-c*L*W*cos(W)+m*g-3*B*((d+x(I)-L*W*sin(W*t(I))).^(-4)-(d-x(I)-L*W*sin(W*t(I))).^(-4)));
With that your code runs just fine. However, it is far from optimized and it runs relatively slow. I have a powerful machine and it still takes a long time to run for me. I suggest you reduce your time step to something more sensible, at least when you are still trying your code. If you really need that kind of precision, first make sure your code runs fine then when it is ready let it run at full precision and go have a coffee while your computer is doing the work.
The snippet below is the loop part of your code with the correct assignment for xddot. I also added a simple progress bar so you can see that your code is doing something.
hw = waitbar(0,'Please wait...') ;
npt = length(t)-1 ;
for I = 1 : npt
xddot =-1/m*(c*xdot(I)-c*L*W*cos(W)+m*g-3*B*((d+x(I)-L*W*sin(W*t(I))).^(-4)-(d-x(I)-L*W*sin(W*t(I))).^(-4)));
xdot(I+1) = xdot(I)+xddot*dt;
x(I+1) = x(I)+xdot(I+1)*dt ;
pcdone = I / npt ;
waitbar(pcdone,hw,[num2str(pcdone*100,'%5.2f') '% done'])
end
close(hw)
I strongly suggest you reduce your time step to dt = 1e-3; until you are satisfied with everything else.
In the final version, you can remove or comment the calls to the waitbar as it slows down things too.
I am trying to run a program that opens a webcam, takes a screenshot, processes it, and shows the output. My code runs correctly and I am getting output, but when I close the output window I get this error every-time:
Matlab System Error: Matlab has encountered an internal problem and needs to close.
As I am new to Matlab can anyone help me? I am using Windows 8 operating system and Matlab R2013a.
This is the code:
clear all;
close all;
clc;
video=videoinput('winvideo',1);
preview(video);
while(true)
data=getsnapshot(video);
R=data(:,:,1);
G=data(:,:,2);
B=data(:,:,3);
for i=1:768
for j=1:1024
if(R(i,j)<128)
out(i,j)=1;
else
out(i,j)=0;
end
end
end
cla; % Prevent stuffing too many images into the axes.
imshow(out);
drawnow;
end
Here's some simpler code that replicates the error on Windows or on Mac for me (R2013b, built-in FaceTime HD camera):
clear all;
close all;
% video = videoinput('macvideo',1);
video = videoinput('winvideo',1);
while true
data = getsnapshot(video);
cla;
imshow(data);
drawnow;
end
Run the above and close the the window after it draws the image and you may be able to get it to crash. The strange thing is that after I reliably made it crash a few times it stopped doing it.
What is going on?
The fact that the error went away randomly for me makes me suspect some sort of race condition. You code isn't particularly correct, but Matlab shouldn't be crashing hard like this, so it should be reported as a bug.
How can you fix this?
The problem is that you're closing a window that is being drawn to inside of an infinite while loop. You need to break the while loop when the figure is closed. And you might also want to perform some cleanup such as deleting the video object. Here's some nice fast code that shouldn't produce an error :
clear all;
close all;
clc;
if ispc
video = videoinput('winvideo',1);
elseif ismac
video = videoinput('macvideo',1);
else
video = videoinput(imaq.VideoDevice);
end
% preview(video);
% Create figure and get handle to image data
data = getsnapshot(video);
R = data(:,:,1);
out = double(R < 128);
h = imshow(out);
while true
data = getsnapshot(video);
R = data(:,:,1);
out = double(R < 128);
if ishghandle(h) % Only if figure still open
set(h,'CData',out); % Replace image data
else
break;
end
end
delete(video); % Clean up
I have a basic code like this :
parfor i=1:8
[t,y]=ode15s(#rate,tspan,cin,options,i); % the option i is evaluated in the rate function
figure(1)
subplot(3,3,i+1)
plot(t,y)
hold on
end
Will any conflict arise because the variable name y is same in all iterations ?
No, every worker has its unique namespace.
However, a worker cannot open figures that display on the client (thanks for the reminder, #Edric), so everything after the call to ode15s will not produce any useful result.
To move the plotting outside the parfor loop, you can do the following (there are more efficient solutions, this one will work for sure):
tCell = cell(8,1);
yCell = cell(8,1);
parfor i=1:8
[tCell{i},yCell{i}]=ode15s(#rate,tspan,cin,options,i); % the option i is evaluated in the rate function
end
figure(1)
for i=1:8
subplot(3,3,i+1)
plot(tCell{i},yCell{i})
hold on
end
Following on from #Jonas' answer, just a note to point out that if you're using R2013b or later, and you wish to display graphics while waiting for your parallel computations to complete, you could use PARFEVAL, like in this example: http://www.mathworks.co.uk/help/distcomp/examples/parfeval-blackjack.html .