Comments for Doug's Pick of the Week

Comment on Puzzler: Find largest connected island by Tim Davis

Tim Davis — Mon, 08 Sep 2008 00:58:30 +0000

Oh, I’m a bit dyslexic. The code has a variable “west” that should be called “east.” East and West are the same to me, and I always get rows vs columns mixed up too …

The code on the File Exchange will have the right name.

Comment on Puzzler: Find largest connected island by Tim Davis

Tim Davis — Mon, 08 Sep 2008 00:54:56 +0000

The fix is to replace the max(diff(r)) line with:


[ignore b] = sortrows ([diff(r') a(p(r(1:end-1)))'])
b = b (end) ;

I'll post a file on the File Exchange that's commented so you can see what the algorithm is doing. The non-commented code is:


function c = mySolver (a)
[m n] = size (a) ;
N = m*n ;
k = reshape (1:N, m, n) ;
west  = [(k (:,2:n) .* (a (:,1:n-1) == a (:,2:n))) zeros(m,1)] ;
south = [(k (2:m,:) .* (a (1:m-1,:) == a (2:m,:))) ; zeros(1,n)] ;
W = find (west) ;
S = find (south) ;
t = length (W) + length (S) + N ;
A = sparse ([k(W);k(S);(1:N)'], [west(W);south(S);(1:N)'], ones(t,1), N, N) ;
[p q r s] = dmperm (A+A') ;
[ignore b] = sortrows ([diff(r') a(p(r(1:end-1)))'])
b = b (end) ;
c = zeros (m,n) ;
c (p ([r(b) : r(b+1)-1])) = 1 ;

Thanks for pointing out the glitch.

Comment on Puzzler: Find largest connected island by Tim Davis

Tim Davis — Sun, 07 Sep 2008 17:50:28 +0000

Matt,
Good point, thanks for catching that. I missed that in the problem statement.

It’s easy to fix. The size of each component is given by diff(r), where the kth component is nodes p(r(k):r(k+1)-1) where a “node” is an entry in the linear-index order of the image a.

max(diff(r)) just finds the biggest one. It’s a small tweak to pick amongst the ties. I’ll post an update.

Comment on Puzzler: Find largest connected island by Matt Fig

Matt Fig — Sun, 07 Sep 2008 16:29:11 +0000

Tim,

There is a problem in your second code. In the case when a zero block is the same size as a non-zero block, your code sometimes returns the zero block.

a = zeros(4) + triu(ones(4)) + diag([-1 -1 0 0])
vs.
a = zeros(4) + triu(ones(4)) + diag([0 0 -1 -1])

Comment on Advanced MATLAB: Compiling a GUI by Moran

Moran — Sun, 07 Sep 2008 02:03:55 +0000

Hi Chris,
I tried everything I could think of, and have sent several observations about this bug to support, but eventually lost all hope that this bug will be fixed in the immediate future (it has been already 2.5 months since I encountered it).

Fortunately, a great alternative exists! Check out Yair Altman’s “CreateTable.m” code:
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=14225&objectType=file

The examples that Yair supplies make it very easy to learn how to use it, even for someone with no previous experience with Java (like me…). Furthermore, this works great (and compiles) on previous versions of Matlab, so no need to upgrade to R2008x, and you can enjoy the much smaller MCR file size (150MB in 2007a vs. 240MB in 2008a).

Hope this helps,
Moran

Comment on Advanced MATLAB: Compiling a GUI by odessit

odessit — Sat, 06 Sep 2008 10:59:50 +0000

Hello,
I have compiled standalone application with deploytool. It would work fine, but the error is in c:\user\Administrator\AppData\Local\MathWorks\mcr_cache_v78\myprog_…..\toolbox\images\icons\point.png
This icon is missed and everytime the program try to call it, it crashes. Wenn I copy this icon manually to this folder - it works!
My question is how to compile my program together with this necessary icon? I think it must be compiled automatically. Wich previos version of matlab compiler I had no problems.
Thanks very much for help.
Leo

Comment on How our developers make MATLAB faster by Duane Hanselman

Duane Hanselman — Fri, 05 Sep 2008 18:12:30 +0000

FYI…

% strmatch replacements
% strmatch is obsolete, strncmp and strcmp are built in
% case insensitive works too with strncmpi and strcmpi

idx=strmatch(str,strarray); % is replaced by
idx=find(strncmp(str,cellstr(strcell),length(str)));

% note that find( ) can be removed for logical results
% in any of these cases.

idx=strmatch(str,strcell); % is replaced by
idx=find(strncmp(str,strcell,length(str)));

idx=strmatch(str,strarray,’exact’); % is replaced by
idx=find(strcmp(strx,cellstr(strarray)));

idx=strmatch(str,strcell,’exact’); % is replaced by
idx=find(strcmp(strx,strcell));

Comment on How our developers make MATLAB faster by Doug

Doug — Thu, 04 Sep 2008 14:23:31 +0000

Duane,

I just looked, I did not see an m-lint warning against STRMATCH in 2008a. However, I seem to recall what you mention also.

I have entered this into our internal enhancement tracking database.

Thanks,
Doug

Comment on Advanced MATLAB: Compiling a GUI by hashem

hashem — Thu, 04 Sep 2008 07:08:56 +0000

Hi Doug,

I built a GUI and write a help for it in “chm” (compiled HTML file) format, and I can’t find a comment in matlab for openig this file. Is here a comment to opning this
file(s)?

Best regard,
Hashem,

Comment on Puzzler: Find largest connected island by Tim Davis

Tim Davis — Thu, 04 Sep 2008 01:44:18 +0000

I left out the comments in the code, above. Most of the functions should be familiar to most MATLAB users. dmperm is the odd one; you can read more about dmperm and how it works, and look at its source code, here:

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=11740&objectType=FILE