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• MATLAB: Convert two array to a sparse matrix

  - by CziX

  I'm looking for an a command or trick to convert two arrays to a sparse matrix. The two arrays contain x-values and y-values, which gives a coordinate in the cartesian coordinate system. I want to group the coordinates, which if the value is between some value on the x-axes and the y-axes. % MATLAB x_i = find(x > 0.1 & x < 0.9); y_i = find(y > 0.4 & y < 0.8); %Then I want to find indicies which are located in both x_i and y_i Is there an easy way to this little trick?

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• how to build an accumulator array in matlab

  - by schwiz

  I'm very new to matlab so sorry if this is a dumb question. I have to following matrices: im = imread('image.jpg'); %<370x366 double> [y,x] = find(im); %x & y both <1280x1 double> theta; %<370x366 double> computed from gradient of image I can currently plot points one at a time like this: plot(x(502) + 120*cos(theta(y(502),x(502))),y(502) + 120*sin(theta(y(502),x(502))),'*b'); But what I want to do is some how increment an accumulator array, something like this: acc = zeros(size(im)); acc(y,x) = acc(x + 120*cos(theta(y,x)),y + 120*sin(theta(y,x)),'*b')) + 1; It would be nice if the 120 could actually be another matrix containing different radius values as well.

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• Compiling a c++ project using blas (Fortran) in Matlab mex

  - by Yin Zhu

  I am trying to use a package here. I have no problem compiling it under 64-bit Linux as all the Makefiles are already provides. Only minor changes are needed, which I can handle. However, I have a problem compiling it under 64-bit Windows. I have installed gfortran and also compiled BLAS and CBLAS to their static libraries. The problem is that Matlab mex does not support GCC in windows, so I need to use VC 2008 instead. I found in the Makefile this line is to get the final klr_train.mexw64: klr_train.$(MEX_EXT): klr_train.cpp $(MEX) $(MEX_OPTION) klr_train.cpp ../libklr/libklr.cpp $(CBLASDIR)/lib/LINUX/cblas_LINUX.a $(BLASDIR)/blas_LINUX.a -lgfortran I don't know how to execute this line using VC 2008's command line tool cl. As cl obviously does not support -lgfortran, which I think is used to link some library in gfortran to support BLAS.

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• How to get real Integer Overflows in Matlab/Octave

  - by marvin2k

  Hi there. I'm working on a verification-tool for some VHDL-Code in Matlab/Octave. Therefore I need datatypes which generate "real" overflows: intmax('int32') + 1 ans = -2147483648 Lateron, it would be helpfull if i can define the bitwidth of a variable... But that is not so important... When I build a C-like example, where a variable gets increased until it's smaller than zero, it spins forever and ever... test = int32(2^30); while (test > 0) test = test + int32(1); end Another approach i tried was a custom "overflow"-routine which was called everytime after a number is changed. This approach was painfully slow, not practicable and not working in all cases at all...

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• annotation in matlab plot

  - by Tim

  Hi, I just wonder how to add annotation in matlab plot? Here is my code: plot(x,y); annotation('textarrow',[x, x+0.05],[y,y+0.05],'String','my point','FontSize',14); But the arrow points to the wrong place. How can I fix it? And any better idea for annotating a plot? Thanks and regards! EDIT: I just saw from the help document: annotation('line',x,y) creates a line annotation object that extends from the point defined by x(1),y(1) to the point defined by x(2),y(2), specified in normalized figure units. In my code, I would like the arrow pointing to the point (x,y) that is drawn by plot(), but annotation interprets the values of x and y as in normalized figure units. So I think that is what causes the problem. How can I specify the correct coordinates to annotation?

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• I have a having a a matrix index bounds in matlab

  - by Ben Fossen

  I keep getting the error( this is in Matlab) Attempted to access r(0,0); index must be a positive integer or logical. Error in == Romberg at 15 I ran it with Romberg(1.3, 2.19,8) I think the problem is the statment is not logical because I made it positive and still got the same error. anyone got some ideas of what i could do? function Romberg(a, b, n) h = b - a; r = zeros(n,n); for i = 1:n h = h/2; sum1 = 0; for k = 1:2:2^(i) sum1 = sum1 + f(a + k*h); end r(i,0) = (1/2)*r(i-1,0) + (sum1)*h; for j = 1:i r(i,j) = r(i,j-1) + (r(i,j-1) - r(i-1,j-1))/((4^j) - 1); end end disp(r); end function f_of_x = f(x) f_of_x = sin(x)/x; end

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• How to format output using MATLAB's num2str

  - by Doresoom

  I'm trying to ouput an array of numbers as a string in MATLAB. I know this is easily done using num2str, but I wanted commas followed by a space to separate the numbers, not tabs. The array elements will at most have resolution to the tenths place, but most of them will be integers. Is there a way to format output so that unnecessary trailing zeros are left off? Here's what I've managed to put together: data=[2,3,5.5,4]; datastring=num2str(data,'%.1f, '); datastring=['[',datastring(1:end-1),']'] which gives the output: [2.0, 3.0, 5.5, 4.0] rather than: [2, 3, 5.5, 4] Any suggestions? EDIT: I just realized that I can use strrep to fix this by calling datastring=strrep(datastring,'.0','') but that seems even more kludgey than what I've been doing.

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• Last in First out UDP structure in MatLab.

  - by D Zondervan

  I am using MatLabs UDP function in their instrument control toolbox to send data packets from one computer to another. The first computer is constantly updating data values and sending them to the other computer, and I want that computer to be able to query the first one for the most recent values whenever it needs them. However, the default implementation of the UDP send and receive in MatLab is a FIFO structure- the first packet I send is the first the other computer receives when they execute the "fscanf" function. I want the last packet I sent to be the one the fscanf function returns. Is this possible or do I need to use a different protocol?

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• Does MATLAB perform tail call optimization?

  - by Shea Levy

  I've recently learned Haskell, and am trying to carry the pure functional style over to my other code when possible. An important aspect of this is treating all variables as immutable, i.e. constants. In order to do so, many computations that would be implemented using loops in an imperative style have to be performed using recursion, which typically incurs a memory penalty due to the allocation a new stack frame for each function call. In the special case of a tail call (where the return value of a called function is immediately returned to the callee's caller), however, this penalty can be bypassed by a process called tail call optimization (in one method, this can be done by essentially replacing a call with a jmp after setting up the stack properly). Does MATLAB perform TCO by default, or is there a way to tell it to?

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• MATLAB fill area between lines

  - by dustynrobots

  I'm trying to do something similar to what's outlined in this post: MATLAB, Filling in the area between two sets of data, lines in one figure but running into a roadblock. I'm trying to shade the area of a graph that represents the mean +/- standard deviation. The variable definitions are a bit complicated but it boils down to this code, and when plotted without shading, I get the screenshot below: x = linspace(0, 100, 101)'; mean = torqueRnormMean(:,1); meanPlusSTD = torqueRnormMean(:,1) + torqueRnormStd(:,1); meanMinusSTD = torqueRnormMean(:,1) - torqueRnormStd(:,1); plot(x, mean, 'k', 'LineWidth', 2) plot(x, meanPlusSTD, 'k--') plot(x, meanMinusSTD, 'k--') But when I try to implement shading just on the lower half of the graph (between mean and meanMinusSTD) by adding the code below, I get a plot that looks like this: fill( [x fliplr(x)], [mean fliplr(meanMinusSTD)], 'y', 'LineStyle','--'); It's obviously not shading the correct area of the graph, and new near-horizontal lines are being created close to 0 that are messing with the shading. Any thoughts? I'm stumped.

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• Saving html page from MATLAB web browser

  - by yuk

  Following this question I get a message on the retrieved page that "Your browser does not support JavaScript so some functionality may be missing!" If I open this page with web(url) in MATLAB web browser and accept certificate (once per session), the page opens properly. How can I save the page source from the browser with a script? Or from system browser? Or may be there is a way to get that page even without browser? url='https://cgwb.nci.nih.gov/cgi-bin/hgTracks?position=chr7:55054218-55242525';

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• to connect matlab with java

  - by user304005

  Through the below given code I was able to connect to matlab. But I was not able to execute the script file containing matlab code...Please help me to modify the code so as to execute the matlab code.... Here luck2 is a .m file.... import java.io.InputStreamReader; import java.io.*; public class matlab { private static File myMATLABScript; public static String runScript(File luck2) { String output = "" ; String error = ""; try { String commandToRun ="C:\\Program Files\\MATLAB\\R2009a\\bin\\matlab -nodisplay <" + "Z:\\sem\\java\\luck2"; //String commandToRun = "matlab -nosplash -r myMATLABScript -nodisplay -nodesktop < " + opentxt; System.out.println(commandToRun); Process p = Runtime.getRuntime().exec(commandToRun); String s; BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream())); BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream())); System.out.println("\nHere is the standard output of the command:\n"); while ((s = stdInput.readLine()) != null) { System.out.println("haiiiiiiiiiiii"); output = s + "\n"; System.out.println(s); } while ((s = stdError.readLine()) != null) { error = s + "\n"; System.out.println(s); } } catch (Exception e) { System.out.println("exception happened here what I know:"); e.printStackTrace(); System.exit(-1); } return output + error; } public static void main(String[] args) throws IOException { matlab m = new matlab(); matlab.runScript(myMATLABScript); //matlab.runScript(); } }

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• recursive function's summation in MATLAB

  - by lucky

  B=[1 1 1 1 1 1....1] % vector of length N elements Xk= sin(2*pi/16) i need to find function alpha(l,k) which is having two variables l and k and a condition given that alpha(l,0)=alpha(l,-1)=alpha(l,-2)......=alpha(l,-(N-1))=0 i.e no matter what value of l ,alpha = 0 for past values A= input('no of iterations'); % no. of iterations user want N=input('N values of alpha:') alpha1=[]; for k=0:A-1 l=0:N-1 % need 10 separate alpha values for every k, which goes from 0 to A-1 alpha(l,k)= Xk + summation( B(j)*alpha(l,k-j)) % as summation goes from j=1 to N alpha1=[alpha1 alpha] end; could anyone please help me to solve this recursive function, i am new to matlab. alpha

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• Audio Detection in Matlab

  - by insane-36

  I am writing a matlab code that would be able to read the audio file and then compare it to the another audio and recognize if those audio are the voice of the same person. In both type of the audio, would have the same word utterance and the audio is about 1 minutes long. I have come to know that the approach of sliding windows using hamming window would work best on this approach but have a very little idea on this. The simple code to read an audio file and then display a portion of 10s is as below : [x,fs, nbits]= wavread('01-AudioTrack 01.wav'); subplot(211) plot(x) title('Entire Wave') smallRange = 1:100000; subplot(212) plot(smallRange,x(smallRange)) How do I make Hamming window each of 10ms in this case and what approaches should I take to deal with this problem ?

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• Making a textfile into a list in matlab?

  - by Ben Fossen

  I have a textfile and would like to import it onto Matlab and make it a list Person1 name = steven grade = 11 age= 17 Person2 name = mike grade = 9 age= 15 Person3 name = taylor grade = 11 age= 17 There are a few hundred entries like these above. Each are seperated by a blank line I was thinking I could scan the text and make the information between each blank line into an item in the list. I also would like to be able to look up each person by name once I have a list like the one below. I want something like x = [Person1 Person2 Person3 name = steven name = mike name = taylor grade = 11 grade = 9 grade = 11 age = 17 age = 15 age = 17] This seems very straight forward but I have been having trouble with this so far, I may be overlooking something. anyone have any ideas or advice?

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• MATLAB Magical Mystery timing behavior

  - by Jacob Lyles

  I am experiencing some very odd timing behavior from a function I wrote. If I wrap my function inside another empty container function, it gets a 3x speedup. > tic; foo(args); toc time elapsed: ~140 seconds >tic; bar(args); toc time elapsed: ~35 seconds Here's the kicker - the definition of bar(): define bar(args) foo(args) end Is there some sort of optimization that gets triggered in MATLAB for nested function calls? Should I be adding a dummy function to every function that I write?

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• MATLAB - Delete elements of binary files without loading entire file

  - by Doresoom

  This may be a stupid question, but Google and MATLAB documentation have failed me. I have a rather large binary file (10 GB) that I need to open and delete the last forty million bytes or so. Is there a way to do this without reading the entire file to memory in chunks and printing it out to a new file? It took 6 hours to generate the file, so I'm cringing at the thought of re-reading the whole thing. EDIT: The file is 14,440,000,000 bytes in size. I need to chop it to 14,400,000,000.

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• Creating matrix of maximum values indices in MATLAB

  - by Gacek

  Using MATLAB, I have an array of values of size 8 rows x N columns. I need to create a matrix of the same size, that counts maximum values in each column and puts 1 in the cell that contains maximum value, and 0 elsewhere. A little example. Lets assume we have an array of values D: D = 0.0088358 0.0040346 0.40276 0.0053221 0.017503 0.011966 0.015095 0.017383 0.14337 0.38608 0.16509 0.15763 0.27546 0.25433 0.2764 0.28442 0.01629 0.0060465 0.0082339 0.0099775 0.034521 0.01196 0.016289 0.021012 0.12632 0.13339 0.11113 0.10288 0.3777 0.19219 0.005005 0.40137 Then, the output matrix for such matrix D would be: 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 Is there a way to do it without catching vector of indices from max function and then putting ones in the right place using for loop?

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• matlab constant anonymous function returns only one value instead of an array

  - by Filo

  I've been searching the net for a couple of mornings and found nothing, hope you can help. I have an anonymous function like this f = @(x,y) [sin(2*pi*x).*cos(2*pi*y), cos(2*pi*x).*sin(2*pi*y)]; that needs to be evaluated on an array of points, something like x = 0:0.1:1; y = 0:0.1:1; w = f(x',y'); Now, in the above example everything works fine, the result w is a 11x2 matrix with in each row the correct value f(x(i), y(i)). The problem comes when I change my function to have constant values: f = @(x,y) [0, 1]; Now, even with array inputs like before, I only get out a 1x2 array like w = [0,1]; while of course I want to have the same structure as before, i.e. a 11x2 matrix. I have no idea why Matlab is doing this...

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• Changeing scaling of Matlab Figure

  - by Phil

  Hi, I have a figure that displays 20.000 points on the x-axis. So it labels the x-axis from 0 .. 20.000. However, now I would like to scale it form 0 to 50. But when I try to do this in the plot window it just shows me the first 50 points, instead of changeing the scale. Is there any straightforward way to do that in Matlab? Many thanks for your help!

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• Default Arguments in Matlab

  - by Scott

  Hello. Is it possible to have default arguments in Matlab? For instance, here: function wave(a,b,n,k,T,f,flag,fTrue=inline('0')) I would like to have the true solution be an optional argument to the wave function. If it is possible, can anyone demonstrate the proper way to do this? Currently, I am trying what I posted above and I get: ??? Error: File: wave.m Line: 1 Column: 37 The expression to the left of the equals sign is not a valid target for an assignment. Thanks!

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• Matlab Question - Principal Component Analysis

  - by Jack

  I have a set of 100 observations where each observation has 45 characteristics. And each one of those observations have a label attached which I want to predict based on those 45 characteristics. So it's an input matrix with the dimension 45 x 100 and a target matrix with the dimension 1 x 100. The thing is that I want to know how many of those 45 characteristics are relevant in my set of data, basically the principal component analysis, and I understand that I can do this with Matlab function processpca. Could you please tell me how can I do this? Suppose that the input matrix is x with 45 rows and 100 columns and y is a vector with 100 elements.

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• MATLAB: draw centroids

  - by Myx

  Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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• How to deal with name/value pairs of function arguments in MATLAB

  - by Richie Cotton

  I have a function that takes optional arguments as name/value pairs. function example(varargin) % Lots of set up stuff vargs = varargin; nargs = length(vargs); names = vargs(1:2:nargs); values = vargs(2:2:nargs); validnames = {'foo', 'bar', 'baz'}; for name = names validatestring(name{:}, validnames); end % Do something ... foo = strmatch('foo', names); disp(values(foo)) end example('foo', 1:10, 'bar', 'qwerty') It seems that there is a lot of effort involved in extracting the appropriate values (and it still isn't particularly robust again badly specified inputs). Is there a better way of handling these name/value pairs? Are there any helper functions that come with MATLAB to assist?

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• Find location of current m-file in Matlab

  - by Jordi

  I'm working on my Matlab code in a number of different locations and it would really help if I could make the code aware of its location on the computer. I think there is a function that gives me exactly this information, but I can't remember what it is called or find it on Google. The idea is that I have a function myFunc that needs a file in its own directory, which can be in different locations on different computers. So in myFunc I want to do something like this: dir = theFunctionImLookingFor; system(fullfile(dir, 'someApp.exe')); (it could also be that the function I'm looking for doesn't return the directory, but the directory + m-file name, but that makes little difference to me) Thanks for any help!

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