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• spike in my inverse fourier transform

  - by Jon

  I am trying to compare two data sets in MATLAB. To do this I need to filter the data sets by Fourier transforming the data, filtering it and then inverse Fourier transforming it. When I inverse Fourier transform the data however I get a spike at either end of the red data set (picture shows the first spike), it should be close to zero at the start, like the blue line. I am comparing many data sets and this only happens occasionally. I have three questions about this phenomenon. First, what may be causing it, secondly, how can I remedy it, and third, will it affect the data further along the time series or just at the beginning and end of the time series as it appears to from the picture. Any help would be great thanks.

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• Interpolating 2d data that is piecewise constant on faces

  - by celil

  I have an irregular mesh which is described by two variables - a faces array that stores the indices of the vertices that constitute each face, and a verts array that stores the coordinates of each vertex. I also have a function that is assumed to be piecewise constant over each face, and it is stored in the form of an array of values per face. I am looking for a way to construct a function f from this data. Something along the following lines: faces = [[0,1,2], [1,2,3], [2,3,4] ...] verts = [[0,0], [0,1], [1,0], [1,1],....] vals = [0.0, 1.0, 0.5, 3.0,....] f = interpolate(faces, verts, vals) f(0.2, 0.2) = 0.0 # point inside face [0,1,2] f(0.6, 0.6) = 1.0 # point inside face [1,2,3] The manual way of evaluating f(x,y) would be to find the corresponding face that the point x,y lies in, and return the value that is stored in that face. Is there a function that already implements this in scipy (or in matlab)?

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• Sudoku solver evaluation function

  - by Rich

  Hi, So I'm trying to write a simple genetic algorithm for solving a sudoku (not the most efficient way, I know, but it's just to practice evolutionary algorithms). I'm having some problems coming up with an efficient evaluation function to test if the puzzle is solved or not and how many errors there are. My first instinct would be to check if each row and column of the matrix (doing it in octave, which is similar to matlab) have unique elements by ordering them, checking for duplicates and then putting them back the way they were, which seems long winded. Any thoughts? Sorry if this has been asked before...

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• Faster projected-norm (quadratic-form, metric-matrix...) style computations

  - by thekindamzkyoulike

  I need to perform lots of evaluations of the form X(:,i)' * A * X(:,i) i = 1...n where X(:,i) is a vector and A is a symmetric matrix. Ostensibly, I can either do this in a loop for i=1:n z(i) = X(:,i)' * A * X(:,i) end which is slow, or vectorise it as z = diag(X' * A * X) which wastes RAM unacceptably when X has a lot of columns. Currently I am compromising on Y = A * X for i=1:n z(i) = Y(:,i)' * X(:,i) end which is a little faster/lighter but still seems unsatisfactory. I was hoping there might be some matlab/scilab idiom or trick to achieve this result more efficiently?

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• how to remove duplicates but keep the same order?

  - by Ben Fossen

  I have a cell array in Matlab y = { 'd' 'f' 'a' 'g' 'g' 'a' 'w' 'h'} I use unique(y) to get rid of the duplicates but it rearranges the strings in alphabetica order >> unique(y) ans = 'a' 'd' 'f' 'g' 'h' 'w' Like this I want to remove the duplicates but keep the same order. I know I could write a function do do this but was wondering if there was a simpler way using unique to remove duplicates while keeping the same order just with the duplicates removed. I want it to return this >> unique(y) ans = 'd' 'f' 'a' 'g' 'w' 'h'

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• Vectorizing sums of different diagonals in a matrix

  - by reve_etrange

  I want to vectorize the following MATLAB code. I think it must be simple but I'm finding it confusing nevertheless. r = some constant less than m or n [m,n] = size(C); S = zeros(m-r,n-r); for i=1:m-r for j=1:n-r S(i,j) = sum(diag(C(i:i+r-1,j:j+r-1))); end end The code calculates a table of scores, S, for a dynamic programming algorithm, from another score table, C. The diagonal summing is to generate scores for individual pieces of the data used to generate C, for all possible pieces (of size r). Thanks in advance for any answers! Sorry if this one should be obvious...

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• I need to order a list that is dependant on another list. how to change both lists?

  - by Ben Fossen

  I have a Matlab program that generates a list x = 6.1692 8.1863 5.8092 8.2754 6.0891 the program also outputs another list aspl = 680 637 669 599 693. The two lists are on equal length and the first element in list x is related to the first element in list aspl. I need to graph the two lists but want list aspl to be in order from smallest to largest. How would I go about doing this? If I need to move the first element in aspl to position 4 in the list, then the first element of list x also needs to be moved to position 4 in list x. The numbers above are not important they are just examples, the actual program generates hundereds of numbers. for example x = 6.1692 8.1863 5.8092 8.2754 initially aspl = 680 637 669 599 693 after changing aspl to ascending order this is how x should look. x = 5.8092 8.1863 5.8092 6.1692 8.2754 aspl = 599 637 669 680 693

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• Tool to diagonalize large matrices

  - by Xodarap

  I want to compute a diffusion kernel, which involves taking exp(b*A) where A is a large matrix. In order to play with values of b, I'd like to diagonalize A (so that exp(A) runs quickly). My matrix is about 25k x 25k, but is very sparse - only about 60k values are non-zero. Matlab's "eigs" function runs of out memory, as does octave's "eig" and R's "eigen." Is there a tool to find the decomposition of large, sparse matrices? Dunno if this is relevant, but A is an adjacency matrix, so it's symmetric, and it is full rank.

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• plot multi graphs with 2 y axis in 1 graph

  - by lytheone

  Hello, Currently I have a a text file with data at the first row is formatted as follow: time;wave height 1;wave height 2;....... I have column until wave height 19 and rows total 4000 rows. Data in the first column is time in second. From 2nd column onwards, it is wave height elevation which is in meter. I would like to plot the follow: ![alt text][1] on the x axis is time. the left hand side is wave height in m and on the right hand side is the distance between each measurment in a model. inside the graph there are 4 plots, each plot is repersent waveight 1, wave height 2etc at a defined distance related to the right hand side y asix. How would you code this in matlab? I am a begineer, please if you could, it will be very useful to give a bit more explain in your answer! Thank you!!!!!!!!!!

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• head detection from video

  - by Aman Kaushal

  I have to detect heads of people in crowd in real time.For that I detected edge from video using matlab but from edge detected video , how to identify heads that i am unable to do. I used edge detection of video because it is easy to find circle from edged video and detection of head would be easy can anyone help me or suggest me any method for head- detection in real time. I have used VGG head detector and viola jones algorithm but it is only detecting face for small size video not detecting heads for large crowd. Suggestions?

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• n*n blocks and polygons

  - by OSaad

  Hi, this is actually meant to be for a function called roipoly in matlab but it can be considered a general case problem. Roipoly is a function which lets u select a polygon over an image, and returns a binary mask where u can use it to get indices of the desired polygon. (It is just a normal polygon after all). My application (K-Nearest Neighbor) requires that i make n*n blocks out of the data i have (the polygon), i.e. If i have a polygon (a road or a piece of land), i want a n*n square moving over it while avoiding intersection with edges and putting those n*n pixels into some variable. This problem would be a lot easier if i had all my shapes in the form of rectangles, but that unfortunately isn't the case. I might have something going diagonal, circular or just irregular.

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• How to prompt for input using an existing variable in the prompt.

  - by ldigas

  I'm trying to ask the user for a value of some variable, but at the same time, showing him the last value used (at the termination of the program, the values are saved to a file, and loaded at the start of the program). Something like this: Enter new radius value (R=12.6) : ... user enters 12.7 ... Enter new pi value (pi=3.14) : Enter new height value (h=30.0) : Usually I would write the first one with write statement, then read the new one (in Fortran, for example). In MATLAB however, I don't know how to write something out with input statement. Are there some other statements for getting input ?

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• Why is simulink data type conversion block altering the data when it should be typecasting?

  - by Nick

  I am attempting to typecast some data from int32 to single. I first tried using the 'Data Type Conversion' block with single output data type and the Stored Integer option. However, I found that the datatype conversion block is not typecasting the data the way I expect it to. Am I using the block incorrectly, or is it failing to work as it should? temp1 (pre conversion): uint32: 1405695244 single: 1728356810752.000000 binary: 01010011110010010011010100001100 temp2 (post conversion): uint32: 1319604842 single: 1405695232.000000 binary: 01001110101001111001001001101010 By the way, I have gotten around the issue by using an embedded Matlab block to perform the typecasting operation.

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• For loop to extract info from a structure doesn't work?

  - by ZaZu

  I have a structure in matlab that has a value of <1x1 struct>., its name is figurelist. Inside that structure, there is a field called images. Inside images, I have 25 images that have the name img1, img2, img3, ...... , img25. Now I made a for loop to extract those images, I basically did: For K=1:25 image(figurelist.images.imgK) PAUSE(0.25) End This unfortunately doesnt work. I get an error saying : ??? Reference to non-existent field 'imgK'. Is it possible to extract such info using a loop from a structure? Or am I doing something wrong? Thanks.

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• How to write a variable with input ?

  - by ldigas

  the title is somewhat vague, so let me explain I'm trying to ask the user for a value of some variable, but at the same time, showing him the last value used (at the termination of the program, the values are saved to a file, and loaded at the start of the program). Something like this: Enter new radius value (R=12.6) : ... user enters 12.7 ... Enter new pi value (pi=3.14) : Enter new height value (h=30.0) : Usually I would write the first one with write statement, then read the new one (in fortran, for example). In matlab however, I don't know how to write something out with input statement. Are there some other statements for getting input ? All your thoughts on the subject appreciated.

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• Error " Index exceeds Matrix dimensions"

  - by Mola

  Hi experts, I am trying to read an excel 2003 file which consist of 62 columns and 2000 rows and then draw 2d dendrogram from 2000 pattern of 2 categories of a data as my plot in matlab. When i run the script, it gives me the above error. I don't know why. Anybody has any idea why i have the above error? My data is here: http://rapidshare.com/files/383549074/data.xls Please delete the 2001 column if you want to use the data for testing. and my code is here: % Script file: cluster_2d_data.m d=2000; n1=22; n2=40; N=62 Data=xlsread('data.xls','A1:BJ2000'); X=Data'; R=1:2000; C=1:2; clustergram(X,'Pdist','euclidean','Linkage','complete','Dimension',2,... 'ROWLABELS',R,'COLUMNLABELS',C,'Dendrogram',{'color',5})

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• Tidying up a list

  - by Jonas

  I'm fairly sure there should be an elegant solution to this (in Matlab), but I just can't think of it right now. I have a list with [classIndex, start, end], and I want to collapse consecutive class indices into one group like so: This 1 1 40 2 46 53 2 55 55 2 57 64 2 67 67 3 68 91 1 94 107 Should turn into this 1 1 40 2 46 67 3 68 91 1 94 107 How do I do that? EDIT Never mind, I think I got it - it's almost like fmarc's solution, but gets the indices right a=[ 1 1 40 2 46 53 2 55 55 2 57 64 2 67 67 3 68 91 1 94 107]; d = diff(a(:,1)); startIdx = logical([1;d]); endIdx = logical([d;1]); b = [a(startIdx,1),a(startIdx,2),a(endIdx,3)];

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• Comparing two images by corr2 function

  - by user3696860

  I'm trying to compare two images by corr2 function on Matlab, it's not necess getting 1 end of function so I am using a treshold to find best images among template images. But sometimes it evaluate wrong image. How can I process them to find best match? ` temp=[]; for i=1:10 res=sprintf('%d.png',i) yol=fullfile('cember\taslak_cember\',res); a=imread(yol); b=imread('30_1.png'); a=rgb2gray(a); b=rgb2gray(b); a=im2bw(a,0.4); b=im2bw(b,0.4); c=corr2(a,b); temp=[temp c]; end max(temp) `

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• I want to make a 2D color plot showing stress magnitude (S) at very loctaion (x, y) based on continuous color change using limited data sets

  - by Alex Liu

  friends, I have to trouble you as I couldn't find a solution after trying for a long time. I have 3 columns of data. x, y, and the stress value (S) at every point (x, y). I want to generate a 2D color plot displaying continuous color change with the magnitude of the stress (S). The stress values increase from -3*10^4 Pa to 4*10^4 Pa. I only have hundreds of data sets for an area, but I want to see the stress magnitude (read from the color) at every location (x, y). What Matlab command should I use? Thank you very much! I want to make a 2D color plot showing stress magnitude (S) at very loctaion (x, y) based on continuous color change using limited

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• How can you distribute the color intensity of two images using its gradients?

  - by Jeppy-man

  Hello everyone... I am working on an automatic image stitching algorithm using MATLAB. So far, I have downloaded a source code much like the one that I had in mind and so, I'm currently studying how the code work. The problem is, when stitching two or more images together, their color intensity will most probably be different from each other so the stitched seams will be visible to the eye... So, right now, I'm trying to find out how to redistribute their color intensity using the images gradients so that the whole stitched image will have the same color intensity. I hope someone can help me out there and if so, thank you very much...

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• Writing a script for reading many .csv files with similar filenames

  - by wahalulu

  I have several .csv files with similar filenames except a numeric month (i.e. 03_data.csv, 04_data.csv, 05_data.csv, etc.) that I'd like to read into R. I have two questions: Is there a function in R similar to MATLAB's varname and assignin that will let me create/declare a variable name within a function or loop that will allow me to read the respective .csv file - i.e. 03_data.csv into 03_data data.frame, etc.? I want to write a quick loop to do this because the filenames are similar. As an alternative, is it better to create one dataframe with the first file and then append the rest using a for loop? How would I do that?

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• Programmatically get valid switch/case values

  - by craigim

  When MATLAB scans through cases in a switch/case block, does it remember the values that it skips, and is it possible to access that list? I have a few functions with long switch\case block and I would like to have them return a list of valid case values if they make it down to otherwise. For instance, I have a function that returns a set of optical constants for a material. It currently has about 20 different materials and it is growing as I consider new ones. I realize I can brute-force it and just re-type all of the valid cases into a cell array under otherwise and have the function throw an error and return the list of valid responses, but maintaining both lists without errors or laziness creeping in over time is challenging.

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• Generating data on unlevel background

  - by bluejay93

  I want to make an unlevel background and then generate some test data on that using Matlab. I was not clear when I asked this question earlier. So for this simple example for i = 1:10 for j = 1:10 f(i,j)=X.^2 + Y.^2 end end where X and Y have been already defined, it plots it on a flat surface. I don't want to distort the function itself, but I want the surface that it goes onto to be unlevel, changed by some degree or something. I hope that's a little clearer.

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• Need help with artificial neural network

  - by deckard cain

  I have an input data for neural network that consists of 2 vectors with 200 elements, that i got from some program for generating signals. So it is actually 2x200 input to my nnet. As target data, i have one 1x200 vector that i also got from the same program. That is my training data set. I gather as much of those sets as i want so i transfer them to matlab and save them as, for example, set1, set2,.... When i am creating neural net, using newfit function (backropagation algorithm and everyhting else is set by default because i am kind of unexperianced with neural nets so i will have to experiment) i'm creating it using set1 only for example. Then, when i am to train neural net i train it for set1 then load set2 and train for it and so on. so its like this function net = create_fit_net(inputs,targets) numHiddenNeurons = 20; net = newfit(inputs,targets,numHiddenNeurons); net=train(net,inputs,targets); load set2; net=train(net,inputs,targets); load set3; net=train(net,inputs,targets); load set4; net=train(net,inputs,targets); i am using 4 sets of data here and all sets have variables of same name and size. My quesion is, am i doing this the right way, because, when doing simulation in some other m file, i am getting bad results, and every time i get different results. Does it matter if i create network with one set and then train with others too, and does it matter what set do i use to train network 1st? Also, i am confused about the amount of neurons to use (im using in the example 20 but actually i tried 1, 10, 30, 50, 100 200 and even 300 and i get nothing). If you have any suggestions, i'd be glad to take them into consideration. Any help is welcome. thanks in advance

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• Neural Network with softmax activation

  - by Cambium

  This is more or less a research project for a course, and my understanding of NN is very/fairly limited, so please be patient :) ============== I am currently in the process of building a neural network that attempts to examine an input dataset and output the probability/likelihood of each classification (there are 5 different classifications). Naturally, the sum of all output nodes should add up to 1. Currently, I have two layers, and I set the hidden layer to contain 10 nodes. I came up with two different types of implementations 1) Logistic sigmoid for hidden layer activation, softmax for output activation 2) Softmax for both hidden layer and output activation I am using gradient descent to find local maximums in order to adjust the hidden nodes' weights and the output nodes' weights. I am certain in that I have this correct for sigmoid. I am less certain with softmax (or whether I can use gradient descent at all), after a bit of researching, I couldn't find the answer and decided to compute the derivative myself and obtained softmax'(x) = softmax(x) - softmax(x)^2 (this returns an column vector of size n). I have also looked into the MATLAB NN toolkit, the derivative of softmax provided by the toolkit returned a square matrix of size nxn, where the diagonal coincides with the softmax'(x) that I calculated by hand; and I am not sure how to interpret the output matrix. I ran each implementation with a learning rate of 0.001 and 1000 iterations of back propagation. However, my NN returns 0.2 (an even distribution) for all five output nodes, for any subset of the input dataset. My conclusions: o I am fairly certain that my gradient of descent is incorrectly done, but I have no idea how to fix this. o Perhaps I am not using enough hidden nodes o Perhaps I should increase the number of layers Any help would be greatly appreciated! The dataset I am working with can be found here (processed Cleveland): http://archive.ics.uci.edu/ml/datasets/Heart+Disease

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