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• Plotting a grouped 2 dimensional vector in MATLAB

  - by Hossein

  I am trying to make a plot of a 2-dimensional vector (2D Plot). But I don't want all the datapoints to have the same color on the plot. Each datapoint corresponds to a group. I want to have different colors for each group of datapoints. class=[1 3 2 5 2 5 1 3 3 4 2 2 2] says each datapoint belongs to which group X=[x1,y1;x2,y2;x3,y3;.....] the number of these datapoints are the same as the number of elements in the class vector. Now I want to plot these based on colors.

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• Extended maxima transform in Matlab

  - by garvin

  I use imtophat to apply a filter to an m x n array. I then find the local max using imextendedmax(). I get mostly 0's everywhere except for 1's in the general areas where I am expecting a local max. The weird thing is, though, that I don't get just one local max. Instead in these places I get MANY elements with 1's such as 00011100000 00111111000 00000110000 yet the values there are close but NOT equal so I would expect that there would be one that is higher than all of the rest. So I'm wondering a) if this is a bug and how I might fix it and b) how you would choose choose the element of these 1's with the highest value.

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• Special functions in Matlab

  - by favala

  I'm trying to get a picture like the following: http://upload.wikimedia.org/wikipedia/en/e/e6/Airy-3d.svg What am I doing wrong? [x,y]=meshgrid(-1:.1:1,-1:.1:1); surf(x,y,(2*besselj(1,2*pi*sqrt(x.^2+ y.^2)/sqrt(x.^2+ y.^2)).^2) Also... kind of a side note, but if I used ndgrid instead of meshgrid here my x's and y's would switch right?

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• What does ~= mean in MATLAB?

  - by Runner

  I've never seen this operator yet.

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• Drawing a polygon around groups of datapoints in MATLAB

  - by Hossein

  Hi, I have a set of datapoints each of which belongs to a certain cluster(group).I need to draw a polygone around each of these clusters.Does anyone knows how to do it? PS: It doesn't matter if I use or not use the actual datapoints for drawing the polygon. I just need them to be wrapped in a polygon. Thanks

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• How to convert dates to numbers in Matlab

  - by user1297712

  I have some variables like these: a(1)=00:26:00 a(2)=744:32:00 a(3)=8040:33:00 I want to convert them to numbers, so I use the datenum command. The biggest number should be 8040:33:00, but look what happens. datenum(a([1 2 3])) ans = 1.0e+005 * 7.3487 7.3485 7.3486 But if I don´t calculate a(1): datenum(a([2 3],51)) ans = 1.0e+005 * 7.3490 7.3520 That´s the results that I want to get. I think that the problem is that a(2) and a(3) have more than 24hours but I haven´t found any way to solve this problem. Thanks.

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• Getting data into MATLAB from HTTPS

  - by yuk

  Anybody know if it's possible? I'm trying to get the data by using the following code url = 'https://cgwb.nci.nih.gov/cgi-bin/hgTracks'; params = {'org','Human','db','hg18','position','EGFR'}; urltxt = urlread(url,'get',params); but get the error ??? Error using ==> urlread at 111 Error downloading URL. Your network connection may be down or your proxy settings improperly configured. If I substitute https to http, it works, but I get "301 Moved Permanently" page with the above https-link. The link in browser works properly in both cases (redirecting http request). The site does not require any authentication. May be there are other ways than urlread?

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• Plotting a grouped 2 dimensional vevtor in MATLAB

  - by Hossein

  Hi, I am trying to make a plot of a 2-Dimensional vector(2D Plot).But I don't want all the datapoints to have the same color on the plot.Each datapoint corresponds to a group.I want to have different colors for each group of datapoints. class=[1 3 2 5 2 5 1 3 3 4 2 2 2] says each datapoint belongs to which group X=[x1,y1;x2,y2;x3,y3;.....] the number of thes datapoints are the same as the number of elements in th class vector. Now I want to plot these based on colors. Can someone help me? Thanks

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• find lowest neighbor matlab

  - by user1812719

  I am trying to write a function [offset,coffset]=findLowNhbr(map) that for each pixel in a map finds the eight neighbors to the pixel, and returns two matrices with both the row and column offsets to the lowest neighbor (uses the numbers -1, 0 and 1). Border pixels are given 0 offsets for both the row and column, since they do not have neighbors. Here is what I think the general plan for this function should be: For each point, find the eight nearest neighbors. If the neighbor is lower than the point, return -1 If the neighbor is at the same elevation as the point, return 0 If the neighbor is higher than the point, return +1 Store these offsets in two matrices. I am at a complete loss as to where to start, so any advice or questions are welcome!

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• Problem using find function in Matlab

  - by Peter Etchells

  Hi all, I have two arrays of data that I'm trying to amalgamate. One contains actual latencies from an experiment in the first column (e.g. 0.345, 0.455... never more than 3 decimal places), along with other data from that experiment. The other contains what is effectively a 'look up' list of latencies ranging from 0.001 to 0.500 in 0.001 increments, along with other pieces of data. Both data sets are X-by-Y doubles. What I'm trying to do is something like... for i = 1:length(actual_latency) row = find(predicted_data(:,1) == actual_latency(i) full_set(i,1:4) = [actual_latency(i) other_info(i) predicted_info(row,2)... predicted_info(row,3)]; end ...in order to find the relevant row in predicted_data where the look up latency corresponds to the actual latency. I then use this to created an amalgamated data set, full_set. I figured this would be really simple, but the find function keeps failing by throwing up an empty matrix when looking for an actual latency that I know is in predicted_data(:,1) (as I've double-checked during debugging). Moreover, if I replace find with a for loop to do the same job, I get a similar error. It doesn't appear to be systematic - using different participant data sets throws it up in different places. Furthermore, during debugging mode, if I use find to try and find a hard-coded value of actual_latency, it doesn't always work. Sometimes yes, sometimes no. I'm really scratching my head over this, so if anyone has any ideas about what might be going on, I'd be really grateful.

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• Iterating through struct fieldnames in MATLAB.

  - by Noio

  My question is easily summarized as: "Why does the following not work?" teststruct = struct('a',3,'b',5,'c',9) fields = fieldnames(teststruct) for i=1:numel(fns) fns(i) teststruct.(fns(i)) end output: ans = 'a' ??? Argument to dynamic structure reference must evaluate to a valid field name. Especially since teststruct.('a') does work. And fns(i) prints out ans = 'a'. I can't get my head around it.

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• Plot overlaps in matlab

  - by ZaZu

  Hey there, I got a strange problem that the plot overlaps in the graph, but not in the image. I am sure I didnt leave hold on somewhere or else it will overlap in the image itself as well. Here is a sample : Any ideas ? Thanks

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• MATLAB - Index exceeds matrix dimensions

  - by Jessy

  Hi I have problem with matrix.. I have many .txt files with different number of rows but have the same number of column (1 column) e.g. s1.txt = 1234 rows s2.txt = 1200 rows s2.txt = 1100 rows I wanted to combine the three files. Since its have different rows .. when I write it to a new file I got this error = Index exceeds matrix dimensions. How I can solved this problem? .

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• Problem with loop MATLAB

  - by Jessy

  no time scores 1 10 123 2 11 22 3 12 22 4 50 55 5 60 22 6 70 66 . . . . . . n n n Above a the content of my txt file (thousand of lines). 1st column - number of samples 2nd column - time (from beginning to end ->accumulated) 3rd column - scores I wanted to create a new file which will be the total of every three sample of the scores divided by the time difference of the same sample. e.g. (123+22+22)/ (12-10) = 167/2 = 83.5 (55+22+66)/(70-50) = 143/20 = 7.15 new txt file 83.5 7.15 . . . n so far I have this code: fid=fopen('data.txt') data = textscan(fid,'%*d %d %d') time = (data{1}) score= (data{2}) for sample=1:length(score) ..... // I'm stucked here .. end ....

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• Matlab Error- fplot();

  - by udsha

  >> fplot(fh,[-2 4]) ??? Undefined function or variable "e". Error in ==> myfun at 3 Y(:,2) = e(:).^x; Error in ==> fplot at 102 x = xmin; y = feval(fun,x,args{4:end}); I tried to plot two function using this m file. function Y = myfun(x) Y(:,1) = 3*x; Y(:,2) = e(:).^x;

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• Graphing special functions in Matlab (2D Bessel)

  - by favala

  I'm trying to essentially get something like this where I can see clear ripples at the base but otherwise it's like a Gaussian: This is kind of unsatisfactory because the ripples aren't very noticeable, it has a very gritty quality that obscures the image a bit, and if you move the graph so that it's just in 2D (so it looks like a circle) I'm not even sure if it's quite like how it should be (the concentric circles seem to be more evenly spaced in the real thing). So, is there a better way to do this? a = 2*pi; [X Y] = meshgrid(-1:0.01:1,-1:0.01:1); R = sqrt(X.^2+Y.^2); f = (2*besselj(1,a*R(:))./R(:)).^2; mesh(X,Y,reshape(f,size(X))); axis vis3d;

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• MATLAB pdist function

  - by James

  Hi, I am using the pdist command to find the distance between x and y coordinates stored in a matrix. X = [100 100; 0 100; 100 0; 500 400; 300 600;]; D = pdist(X,'euclidean') Which returns a 15 element vector. : [0.734979755525412 3.40039811339820 2.93175207511321 1.83879677592575 2.40127440268306 2.75251513299386 2.21488402640753 1.10610649500317 1.81674017301699 0.903207751535635 1.99116952754924 1.05069952386082 1.24122819418333 1.08583377275532 1.38729428638035] Is there a way to associate these distances with the coordinates they were derived from, i.e. store them in a matrix with the general row form: [Length xcoordinate1 ycoordinate1 xcoordinate2 ycoordinate2] Where there is a row for each length found? Thanks in advance

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• matlab: simple matrix filtering - group size

  - by Art

  I have a huuuge matrix storing information about X and Y coordinates of multiple particle trajectories , which in simplified version looks like that: col 1- track number; col 2- frame number; col 2- coordinate X; col 3- coordinate Y for example: A = 1 1 5.14832 3.36128 1 2 5.02768 3.60944 1 3 4.85856 3.81616 1 4 5.17424 4.08384 2 1 2.02928 18.47536 2 2 2.064 18.5464 3 1 8.19648 5.31056 3 2 8.04848 5.33568 3 3 7.82016 5.29088 3 4 7.80464 5.31632 3 5 7.68256 5.4624 3 6 7.62592 5.572 Now I want to filter out trajectories shorter than lets say 2 and keep remaining stuff like (note renumbering of trajectories): B = 1 1 5.14832 3.36128 1 2 5.02768 3.60944 1 3 4.85856 3.81616 1 4 5.17424 4.08384 2 1 8.19648 5.31056 2 2 8.04848 5.33568 2 3 7.82016 5.29088 2 4 7.80464 5.31632 2 5 7.68256 5.4624 2 6 7.62592 5.572 How to do it efficiently? I can think about some ideas using for loop and vertcat, but its the slowest solution ever :/ Thanks!

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• matlab: putting a circled number onto a graph

  - by Jason S

  I want to put a circled number on a graph as a marker near (but not on) a point. Sounds easy, but I also want to be invariant of zoom/aspect ratio changes. Because of this invariant, I can't draw a circle as a line object (without redrawing it upon rescale); if I use a circle marker, I'd have to adjust its offset upon rescale. The simplest approach I can think of is to use the Unicode or Wingdings characters ① ② ③ etc. in a string for the text() function. But unicode doesn't seem to work right, and the following sample only works with ① and not for the other numbers (which yield rectangle boxes): works: clf; text(0.5,0.5,char(129),'FontName','WingDings') doesn't work (should be a circled 2): clf; text(0.5,0.5,char(130),'FontName','WingDings') What gives, and can anyone suggest a workaround?

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• MATLAB syntax of (:)

  - by user198729

  >> I=[2 1 3;3 2 4] I = 2 1 3 3 2 4 >> I(:) ans = 2 3 1 2 3 4 >> I(1:2) ans = 2 3 >> Why the first call I(:) returns a vector while the second I(1:2) doesn't which is essentially the same as I(:)?

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• 3x3 Average filter in matlab

  - by turingcomplete

  I've written code to smooth an image using a 3x3 averaging filter, however the output is strange, it is almost all black. Here's my code. function [filtered_img] = average_filter(noisy_img) [m,n] = size(noisy_img); filtered_img = zeros(m,n); for i = 1:m-2 for j = 1:n-2 sum = 0; for k = i:i+2 for l = j:j+2 sum = sum+noisy_img(k,l); end end filtered_img(i+1,j+1) = sum/9.0; end end end I call the function as follows: img=imread('img.bmp'); filtered = average_filter(img); imshow(uint8(filtered)); I can't see anything wrong in the code logic so far, I'd appreciate it if someone can spot the problem.

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• MATLAB help required function root

  - by programmeur

  Dear All, I have made an program, function bisection; x1=input('enter the first value=') x2=input('enter the second value=') %f3=[]; for x=1:20 %x=1; x3=(x1+x2)/2; while x3-x1 >= 0.001 f3(x)=x3^3 + x3^2 - 3*x3 - 3; f1(x)=x1^3 + x1^2 - 3*x1 - 3; if ((f3(x)*f1(x)) < 0) x2=x3; else x1=x3; end break end format long f3' disp('The root is found to be ='); x3 end . . . . . program calculate function of interval (x1, x2) given by user, my program compile and execute but little stupid repetition until for loop complete, i want to stop further printing loop when desired value is achieved with while condition is used.

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• Weighted random numbers in MATLAB

  - by yuk

  How to randomly pick up N numbers from a vector a with weight assigned to each number? Let's say: a = 1:3; % possible numbers weight = [0.3 0.1 0.2]; % corresponding weights In this case probability to pick up 1 should be 3 times higher than to pick up 2. Sum of all weights can be anything.

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• radio button group matlab

  - by vijisai

  i have two set of button groups. first button groups has two radio buttons and second group has four radio buttons. if button 1 is selected in group1 and any one from the group 2. similarly for button2 in group 1 and any one from group2, respective function calls must be made on click of push button with these combinations. how to do it. there will be 8 separate function calls for their respective combinations. how to do the combination of button groups. switch case or if else statement did not work out?? kindly help.

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• Help in optimizing a for loop in matlab

  - by HH

  I have a 1 by N double array consisting of 1 and 0. I would like to map all the 1 to symbol '-3' and '3' and all the 0 to symbol '-1' and '1' equally. Below is my code. As my array is approx 1 by 8 million, it is taking a very long time. How to speed things up? [row,ll] = size(Data); sym_zero = -1; sym_one = -3; for loop = 1 : row if Data(loop,1) == 0 Data2(loop,1) = sym_zero; if sym_zero == -1 sym_zero = 1; else sym_zero = -1; end else Data2(loop,1) = sym_one; if sym_one == -3 sym_zero = 3; else sym_zero = -3; end end end

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