Matlab

Script from a line number

vortexshedding@hotmail.com — Wed, 09 Jul 2008 00:07:41 GMT

Hi! Is there a way to run a script from a specific line number till the end? Or at least run 1 specific line from a script? Thanks a lot!

repeated measures ANOVA.

vortexshedding@hotmail.com — Fri, 04 May 2007 15:39:40 GMT

Is repeated measures ANOVA implementation in matlab really as dire as it seems? I can't dind any tools that run n-way repeated measures ANOVA. Anyone got any pointers?

Web Scraping & Calendar Conversion

vortexshedding@hotmail.com — Fri, 04 May 2007 15:30:01 GMT

The MATLAB code below takes a big list of myspace band usernames, scrapes the gig information off of each one's website, and sticks it into a single Google Calendar compatible *.csv file.

Future development may include refactoring into Ruby and creation of iCal standard output. Right now, though, it's good enough for my purposes.


% run_the_gig_amalgamating_myspace_scraping_calendar_compatibility_maker.m
% (c) opticsdoug May 2007
% I run this script to load up my massive list of bands, and output
% all their gigs to a Google Calendar compatible *.csv file

% It passes arguments to scrape_shows_to_csv, which in turn
% wraps the functions scrape_shows and shows_to_csv that do all the work.
clc
% This loads up the bandlist, which is just an ascii file with each
% band's myspace name on a new line
listofbands = textread('may_bandlist.m','%s');
% just as easily, you can put in a few bands by hand, like this next line
%listofbands = {'pirex', 'littlevoice','lorettatheband'}

%Here's where I set the output filename
output_filename = 'output.csv';

% And here's where we run the big wrapper function with all the goodies
% inside
scrape_shows_to_csv(listofbands,output_filename)

% And thus the little script ends. On with the show!
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% function scrape_shows_to_csv(listofbands,output_filename)
% (c) opticsdoug May 2007
% This function wraps scrape_shows and shows_to_csv
% Given
% 1) listofbands (a cell array of strings - the myspace bandnames), and
% 2) output_filename (a string of the csv filename we want to build)
% This file will scrape the myspace pages of the named bands, and build a
% *.csv file of all the named bands' gigs. This *.csv file is at least
% compatible with Google Calendar, possibly Outlook or Yahoo!


function scrape_shows_to_csv(listofbands,output_filename)

% Here we call the ScrapeUpcomingShows function for each of the bands in
% our listofbands cell array of strings
% Then we concatenate them into one massive cell array of gigging power
massive_cell_array ={};
for index = 1:length(listofbands)
    disp(listofbands{index})
massive_cell_array = [massive_cell_array; scrape_shows(listofbands{index})];
end

shows_to_csv(massive_cell_array,output_filename);




% function awesome_cell_array = scrape_shows(username)
% (c) opticsdoug May 2007
% some nights I am more nerdy than others
% This matlab script takes a myspace band's username and returns a cell
% array of the following form:
% 'username' 'venue' 'MMM DD YYYY' 'HH:MMP' 'City, State' 'details url'
% with as many of those rows as they have gig entries

function awesome_cell_array = scrape_shows(username)
%username = 'lorettatheband'

s = urlread(['http://www.myspace.com/' username]);

%finds the Upcoming Shows division (profile_bandschedule)
startdivat = strfind(s, '<div id="profile_bandschedule">');
if isempty(startdivat)
    awesome_cell_array = {};
    return
end
l = strfind(s, '</div>');
m = find((l>startdivat));
enddivat = l(m(1));
mydiv = s(startdivat:enddivat);


%pulls out all the venue listings and associated urls
alllinkstarts = strfind(mydiv,'<a href=');
endlinkindices = strfind(mydiv,'</a>');
clear link_array thisvenue
for index = 2:length(alllinkstarts)
    alllinkstarts = strfind(mydiv(1:endlinkindices(index)),'<a href=');
    grabbedstring = mydiv(alllinkstarts(index):endlinkindices(index)+3);
    link_array{index-1} = grabbedstring;
    
    endoftag = strfind(grabbedstring,'>');
    endoftext = strfind(grabbedstring,'</a>');
    
    thisvenue = grabbedstring(endoftag(1)+1:endoftext-1);
    venue_array{index-1} = thisvenue;
end

%pulls out the rest of the text fields, identified by the useful placement
%of </font> tags
fontcloseindices = strfind(mydiv,'</font>');
textdata ={};
for index = 1:length(fontcloseindices)
    allmarkupends = strfind(mydiv(1:fontcloseindices(index)),'>');
    grabbedstring = mydiv(allmarkupends(end)+1:fontcloseindices(index)-1);
    
    %this filter went through a lot of changes - it has to allow for folks
    %who put garbage in for their gig's location, while throwing out a
    %bunch of useless tokens.
    %if or(length(grabbedstring)>2, strcmp(grabbedstring,'?'))
    %if and(length(grabbedstring)>0, index>1)
    if and(mod(index,4)~=1, index~=2)
        textdata = {textdata{:}, grabbedstring};
    end
end


%<span class="nametext">Loretta</span>
nametextstart = strfind(s,'<span class="nametext">')+23;
nametextend = strfind(s(nametextstart:nametextstart+100),'<');
bandname = s(nametextstart:nametextstart+nametextend(1)-2);


%and we mash everything together
reshaped_text = reshape(textdata, 3,[])';
bandnamecells = repmat({bandname}, size(reshaped_text,1),1);

%and viola
awesome_cell_array = reshape({bandnamecells{:},venue_array{:}, reshaped_text{:}, link_array{:}}',length(bandnamecells),[]);



% function shows_to_csv(massive_cell_array,output_filename)
% (c) opticsdoug May 2007
% This matlab function takes a big cell array of strings, as created by
% function scrape_upcoming_shows.m and spits them into a Google Calendar
% readable *.csv file of specified output_filename

function shows_to_csv(massive_cell_array,output_filename)

%matlab file handling garbage - creates or overwrites as necessary
fid = fopen(output_filename ,'w+');
if fid == (-1)
    error('Could not open file %s', output_filename);
end

% Here we go and fix the date and time strings to make them match the
% Outlook *.csv file formatting. I got lucky, and matlab has the internal
% timestamp definitions to process these correctly.
datestrings = {};
timestrings = {};
for index = 1:size(massive_cell_array,1)
    this_datenum = datenum([massive_cell_array{index,3}]);
    outdatstr = datestr(this_datenum,23);
    datestrings{index}=outdatstr;

    this_timenum = datenum([massive_cell_array{index,4}]);
    outtimestr = datestr(this_timenum,14);
    timestrings{index}=outtimestr;
end

% Here we do all the file writing
% notice the tricks for writing comma delimited files:
% 1) all your text cells need to be in quotes
% 2) if your text has quotation marks in it, they need to be doubled
fprintf(fid,'"Subject","Start Date","Start Time","Location","Description"\n');
for index = 1:size(massive_cell_array,1)
fprintf(fid, '"%s","%s","%s","%s","%s"\n',...
    strrep(massive_cell_array{index,1},'"','""'),...
    datestrings{index},...
    strtrim(timestrings{index}),...
    strrep(massive_cell_array{index,5},'"','""'),...
    strrep(massive_cell_array{index,6},'"','""'));
end
fclose(fid);
disp('done')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Processed 880 events.
Successfully imported 880 events.

That's what Google Calendar had to say about a quick test with 144 bands.

Repeated measures ANOVA

vortexshedding@hotmail.com — Wed, 25 Apr 2007 10:07:10 GMT

Is there any way at all to implement n-ways repeated measures ANOVA in Matlab?

matlab - accumulated histogram

vortexshedding@hotmail.com — Mon, 09 Apr 2007 12:59:38 GMT

Hi!

what is called the accumulated histogram of the image?

i need calculated accumulated histogram (normalized).

How do I make this?

vortexshedding@hotmail.com — Mon, 23 Oct 2006 02:20:02 GMT

Hi!
I'm adding tick labels to a plot:


set(gca,'XTickLabel',{'label label','label label','label label'})

and I would like to make them multiline like this:
label
label

How do I make this? I didn't find any solution.
With title I can do like this:


title(sprintf('label\nlabel'))

vortexshedding@hotmail.com — Fri, 08 Sep 2006 12:13:19 GMT

This community looks quite dead, but anyway ;)

Do you know how to solve problem with variable list of output arguments:
output of

gradient(U);

depends on number of dimensions of U. So I have to do

[dX] = gradient(U);
[dX,dY] = gradient(U);
[dX,dY,dZ] = gradient(U);

How to make it general?

Animations (getframe, movie, movie2avi)

vortexshedding@hotmail.com — Sat, 22 Jul 2006 01:51:35 GMT

I have 3 subplots within my figure and I would like to create an avi. Do I need to use the "getframe" command 3 times (once per subplot)? If so, then what is the format of the subsequent "movie" and "movie2avi" commands? I am only familiar with those commands which call a single "getframe" variable, i.e. if F(t) = getframe, then movie(F,1) and movie2avi(F, 'samplemovie.avi').

for t=first_frame:last_frame

subplot(3,1,1)
plotting commands
A(t) = getframe;

subplot(3,1,2)
plotting commands
B(t) = getframe;

subplot(3,1,3)
plotting commands
C(t) = getframe;

end

Is this the correct approach? Is there a better approach? Can I use "getframe" just once for the entire figure instead of 3 times for each subplot? If not, then how can I use the "movie" and "movie2avi" commands for A, B, C all at once (I want 1 single avi file to contain all 3 subplots).

Thanks!

Matlab Tips and Tricks

vortexshedding@hotmail.com — Mon, 22 May 2006 15:27:13 GMT

I am constantly discovering little tricks to get Matlab to run better or do things more easily. I feel like there must be a ton of them that I don't know about. So I will start by sharing a few of mine, and then if you want to comment with some more, that would be awesome.

1. Turn off hyperthreading. This dropped my processing time by 30-40% right off the bat. It does make other programs less responsive, but that can also be fixed by:

2. Setting Matlab's priority to "below normal" (CTRL-ALT-DEL -> task manager -> processes -> Right click on matlab.exe -> Set Priority). I have not had any stability problems with this, and it makes the computer much more usable when Matlab is running full out.

3. If you are running loops (which are good to avoid, but some things are really hard to do with vectors), and you are saving a new result each time, initialize to the proper length first. For example:

N = 1E5;
for count = 1:N
x(count) = count;
end

takes about 60 seconds to run, while putting x = zeros(1,N); in front drops the time to 0.0014 seconds.

4. If you are running a script, and you just want to rerun a part of the code, you can select it with the mouse and press F9. It will run just that part in the command window.

What is the most helpful Matlab tip you know of?

Refresh / Update file modification

vortexshedding@hotmail.com — Sat, 20 May 2006 05:21:30 GMT

I use an external editor to write Matlab doe and after I modify some functions, rerun it .. Matlab tends not to update the changes. I know there is a command that updates these changes as I have used this command before I can't recall what it is ... Any one can help ?

Thanks

word of warning regarding upgrading to Matlab v 14

vortexshedding@hotmail.com — Tue, 11 Apr 2006 02:53:49 GMT

I had the student version 13. I also bought the additional toolboxes optimization and controls about a year ago. I had somehow lost my installation CD and figured it might not be a bad idea to upgrade to student version 14. So I paid $99 plus taxes plus shipping and handling. I get it to install on my computer. I then accessed those "online installs" for those two toolboxes I got last year. Guess what? They tell me it only works for Matlab 13 and if I want to use my toolboxes I gotta pay more money to buy the toolbox installs for version 14 !! The optimization tool box was $60. The Matlab 14 version was $99. I paid $60 January 2005 and you'd think that would work with "future" versions of matlab. Nope!!!

Hence my word of warning:

If you have toolboxes for the student version, they will not work on future upgrades. I confirmed this with the technical support at the mathworks.

Isn't this unfair?

How to Keep an Idiot Busy in Matlab...

vortexshedding@hotmail.com — Wed, 29 Mar 2006 02:52:46 GMT

% How to Keep an Idiot Busy in Matlab
b = uicontrol('Style', 'pushbutton', 'Units', 'normalized', 'Position',[.5 .5 .2 .1], 'String', 'Click Me!');
s = 'set(b, ''Position'',[0.8*rand 0.9*rand .2 .1])';
k = 1000;
while k >0
eval(s);
pause(1);
k = k-1;
end
set(b,'Callback',s);

How do I check if a cell has a variable called 's' ?

vortexshedding@hotmail.com — Mon, 27 Feb 2006 20:59:36 GMT

Hi,

How do I check if a cell has a variable called 's' ? of course I can just call that cell and look on the screen but is there a way to do it in Matlabl ? for example go through all variables in a Cell and strcomp variable{i} with value 's' ? Thanks

Writting to both screen and file

vortexshedding@hotmail.com — Sat, 18 Feb 2006 16:10:09 GMT

Hi, how can I write output to both screen and file quickly ? One method is use both fprintf('something'); then fprintf(fid,'something'). This double the number of lines. I also try to do something like for i = 1:length(fid_vector) fprintf(fid_vector(i),'something') end; ... I hope there's a quicker and more correct method ?

Simple drawing program to smoothen curve

vortexshedding@hotmail.com — Wed, 18 Jan 2006 15:53:00 GMT

Simple drawing program to smoothen curve

Hi, any suggestion on a drawing program produce smoothen contious line , I have graphs with lines which sharp edges and I want to smoothen those. Basically given several points on a graphs, draw a curve through those points ... simple as that.

I was able to do some tricks (in Matlab) with least square procedure to produce smooth curve but the problem is it's not as flexible (e.g., I cannot tell it what point exactly it must pass through) so I am looking for a program that allows me to do so. Please not gimp or photoshop as I don't know how to use them and doubt I can learn their complexity quickly.

Thanks

vortexshedding@hotmail.com — Mon, 19 Dec 2005 17:18:23 GMT

Hello!

In my city:
The price of the DVD with full version MATLAB7 with keygen is $2.5
And for $0.5 you can exchange this DVD to other disk with ANY program, like Photoshop CS, Matlab, Office.... etc.

And this for sale everywere...
This is TERRIBLE!!! but, it is convenient for students.

How much did you pay for MATLAB?

matlab precision

vortexshedding@hotmail.com — Sat, 03 Dec 2005 21:33:22 GMT

While working on my final project for a graduate level engineering class while using matlab I stumbled upon a mind blogging situation on a simple if-else comparison

for i=1:somenumber
if value1 > value2
.......................
else
end;
end;

value1 is a calculated value in my program. value2 is not.

If the value of value1 = value2 (for example: value1 = 1.15 and value2 = 1.15) then the simple if-else statement was still evaluating value1 > value2 value.

So Matlab had determined that 1.15 was bigger than value2. I clearly could not see why at the time until I thought of this:

I had to rectify the situation by introducing something like this:

if abs(value1 - value2) < 0.00000005

The lesson I learned was that MATLAB stored some digit(s) far into the nth decimal place on value1 but did not print them.

I am uncertain about the precision functions in matlab and have inspected them while tackling this issue.

vortexshedding@hotmail.com — Tue, 05 Jul 2005 08:51:52 GMT

Hi guys!
I'm using MATLB7 and I have some trouble in MATLAB GUI programming, and there is no answer for it in Google, so I would be very grateful for your help.

I have made GuidemoMY.fig figure file and its corresponding GuidemoMY.m file was created.
GuidemoMY.fig contains several edit boxes (text fields for user input) which are initialized to some values, and one RUN pushbutton, that has callback function myRun(...) which has to retrieve those edit boxes values.

The problem is, that myRun(..) cannot read those values from 'handles' structure passed to it.
I don't know why, but before the apperance of callback function declaration and body, the 'handles' structure IS recognized, and the command
a = get(handles.figure1Probab,'String');
is successfully evaluated and returns string value of edit box with 'figure1Pribab' tag.
BUT same line INSIDE body of myRun(..) callback (which is successfully called after pressing the RUN button on GUI figure) -- is not evaluated,
and I get "invalid handle object" error, although 'handles' IS NOT EMPTY (I checked it in DEBUG mode).

What the hell is happenning and how can I retrieve the edit box values inside my callback?

Thank you very much!!

excel add-in

vortexshedding@hotmail.com — Fri, 24 Jun 2005 02:51:58 GMT

I have a student copy and the matlab site says student version cannot use the excel add-in.

Is there anyway around this or being able to import data easily from excel into matlab?

Matlab on OS X

vortexshedding@hotmail.com — Fri, 20 May 2005 21:10:14 GMT

So I just got a computer with OS X Tiger (10.4.1) on it, and am having some trouble getting Matlab to go. I am still running R13, which looks like it may not work with OS X on the Mathworks website. But a friends R14SP1 didn't do any better. I have loaded X11, and when I click on the install button, nothing happens.

Any guesses?

fft

vortexshedding@hotmail.com — Thu, 05 May 2005 23:18:27 GMT

Okay, I'm overly confused by this problem, which should be simple, and maybe it's because I'm not sure I completely understand how fft works. So I have this sine wave: x(n) = 2.5 sin(2*pi*n*dt/64), where dt = .1 and n ranges from 0 to 1023 (so that there are 1024 observations and I think that dt means that there are 1024 observations in .1 s).

I'm trying to find the frequency, amplitude and phase and x(n) and then find its Fourier series coefficients. Okay, so I went ahead and applied fft(x). The peak is kind of assymmetric I think because the observation includes more than just one period of a sine wave. Anyway, I multiplied the output by 2/1024 and I looked at the peak. Well, the magnitude of this value isn't 2.5 (more like 1.7) and I think it's because that we have these extra observations, where x(1023) < 0. Also, I thought that the frequency would be at 1/64 -at the peak but it wasn't. So now I'm not even sure I made this list of frequencies correctly. argh. I found the phase using matlab help but I'm not quite sure what it means. As for the Fourier coefficients, isn't the fft*2/N the fourier coefficients? And you just take either the real or imaginary parts? If anyone can help, I'd greatly appreciate it.

update: NM- I figured it out- basically my resolution on the fft was too low and I needed to up the number of points past 1024.

Here's a little code if you have any clue how to help.

dt = .1; %s
n = 0:1:1023; %1024 observations between t = 0 and t = .1 s.

%In the code, x(1) is equal to x_0 at n = 0.
x = 2.5*sin(2*pi*n*dt/64);
fftx = fft(x);
m = fftx;

%determine the phase angle of the harmonic
p = unwrap(angle(fftx));
w = (0:length(fftx)-1)'*100/length(fftx); %the frequencies
m = m*2/length(n); %output of the fft*2/1024

%plot the function
figure(1), subplot(2,1,1), plot(n*dt/1023, x)
ylabel('x_n')
xlabel('Time (s)')
title('Plot of the observed x_n')

figure(2)
subplot(2,1,1), plot(w,abs(m)),
ylabel('Abs. Magnitude'), grid on
xlabel('Frequency [Hertz]')
axis([0 10 0 3])
subplot(2,1,2), plot(w,p*180/pi)
ylabel('Phase [Degrees]'), grid on
xlabel('Frequency [Hertz]')

3d scatter

vortexshedding@hotmail.com — Wed, 06 Apr 2005 17:32:56 GMT

this should be a fairly straightforward question: how would I go about plotting a 3D scatter plot in Matlab? thanks!

vortexshedding@hotmail.com — Tue, 29 Mar 2005 01:46:26 GMT

Anyone know where I can find a MATLAB GS(A) function that does the Gram-Schmidt process on the columns of a matrix? I tried to program it myself...but the loops are infinitely confusing

I was referred here.

vortexshedding@hotmail.com — Tue, 22 Feb 2005 05:21:58 GMT

Hi. I'm relatively new to Matlab and I'm trying to work with GUI pop-ups. What I am attempting to do is create a pop-up message window that provides the user with seven lines of information to verify and two buttons where the user can either confirm or change the information. Unfortunately, all I can find is

msgboxtext=char(text1,text2); uiwait(msgbox('text, 'title')): to get an information pop-up with an "OK" button
and
confirm=menu('information', 'confirm', 'change'): to get an information pop-up with only one line of information and "Confirm" and "Change" buttons

Can you help me?

So far, I have succeeded in making a 7-line MENU. It looks hideous, as you can see.

What do you suggest I do to tidy it up? Ordinarily, I would just accept this, but the problem is, the way I set up my text, it's an 8 x 2 matrix. My placeholder for the last line is a one-space string, but if the user inputs two-digit data values, the box won't work. I considered using a for loop using the length command, but is there an easier way?

Thank you fellow engineers.

homework help

vortexshedding@hotmail.com — Wed, 09 Feb 2005 23:04:18 GMT

I'm having trouble with the following problem. I tried to write a loop so that an error warning would print each time the robot was at a border and would move in the -1 direction (outside of the matrix) but it just stops the loop then I have to start all over again. I'm trying to fix the problem right now but don't know how. Any tips? I'm new to MATLAB but am eager to learn and understand any advice you might have.

I am also offering baked goods in return for your help!

The problem is to write a program to simulate the motion of a robot between a room that us 5 meters long by 5 meters wide. This will be represented by a matrix 5X5 and the robot will move from the coordinate (1,1) to coordinate (5,5). The motion from one block to the next is going to be random and require a direction. For example, a one-dimensional move could be modeled with a code like:

function z=dice_move
% z is a random number generated it could be -> -1 0 1
x=3*rand
x1=ceil(x)
value=[-1 0 1]
z=value(x1)

Taking the assumption that the tobot is free to move backward or forward.

Write the code to do the trip from the initial point to final point. Use the dice_move as part of the movement of the robot.

(a) Include a flowchart to see the planning for the program. This flowchart should be changing as you find problems or better ways to do something.
(b) Write your final code in MATLAB using a script to run the functions created.
(c) The code should start at (1,1) and move until it gets to (5,5). Record the number of times it needs to get to (5,5). The script file should program 50 runs to be able to get a mean about how long it takes usually (mean), the maximum (max), and the minimum.