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• Sorting eigenvectors by their eigenvalues (associated sorting)

  - by fbrereto

  I have an unsorted vector of eigenvalues and a related matrix of eigenvectors. I'd like to sort the columns of the matrix with respect to the sorted set of eigenvalues. (e.g., if eigenvalue[3] moves to eigenvalue[2], I want column 3 of the eigenvector matrix to move over to column 2.) I know I can sort the eigenvalues in O(N log N) via std::sort. Without rolling my own sorting algorithm, how do I make sure the matrix's columns (the associated eigenvectors) follow along with their eigenvalues as the latter are sorted?

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• How do I translate this Matlab bsxfun call to R?

  - by claytontstanley

  I would also (fingers crossed) like the solution to work with R Sparse Matrices in the Matrix package. >> A = [1,2,3,4,5] A = 1 2 3 4 5 >> B = [1;2;3;4;5] B = 1 2 3 4 5 >> bsxfun(@times, A, B) ans = 1 2 3 4 5 2 4 6 8 10 3 6 9 12 15 4 8 12 16 20 5 10 15 20 25 >> EDIT: I would like to do a matrix multiplication of these sparse vectors, and return a sparse array: > class(NRowSums) [1] "dsparseVector" attr(,"package") [1] "Matrix" > class(NColSums) [1] "dsparseVector" attr(,"package") [1] "Matrix" > NRowSums * NColSums (I think) w/o using a non-sparse variable to temporarily store data.

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• Best and simple data structure

  - by anshu

  I am trying to create the below matrix in my vb.net so during processing I can get the match scores for the alphabets, for example: What is the match for A and N?, I will look into my inbuilt matrix and return -2 Similarly, What is the match for P and L?, I will look into my inbuilt matrix and return -3 Please suggest me how to go about it, I was trying to use nested dictionary like this: Dim myNestedDictionary As New Dictionary(Of String, Dictionary(Of String, Integer))() Dim lTempDict As New Dictionary(Of String, Integer) lTempDict.Add("A", 4) myNestedDictionary.Add("A", lTempDict) The other way could be is to read the Matrix from a text based file and then fill the two dimensional array. Thanks.

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• Const operator overloading problems in C++

  - by steigers

  Hello everybody, I'm having trouble with overloading operator() with a const version: #include <iostream> #include <vector> using namespace std; class Matrix { public: Matrix(int m, int n) { vector<double> tmp(m, 0.0); data.resize(n, tmp); } ~Matrix() { } const double & operator()(int ii, int jj) const { cout << " - const-version was called - "; return data[ii][jj]; } double & operator()(int ii, int jj) { cout << " - NONconst-version was called - "; if (ii!=1) { throw "Error: you may only alter the first row of the matrix."; } return data[ii][jj]; } protected: vector< vector<double> > data; }; int main() { try { Matrix A(10,10); A(1,1) = 8.8; cout << "A(1,1)=" << A(1,1) << endl; cout << "A(2,2)=" << A(2,2) << endl; double tmp = A(3,3); } catch (const char* c) { cout << c << endl; } } This gives me the following output: NONconst-version was called - - NONconst-version was called - A(1,1)=8.8 NONconst-version was called - Error: you may only alter the first row of the matrix. How can I achieve that C++ call the const-version of operator()? I am using GCC 4.4.0. Thanks for your help! Sebastian

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• Code Golf: Zigzag pattern scanning

  - by fbrereto

  The Challenge The shortest code by character count that takes a single input integer N (N = 3) and returns an array of indices that when iterated would traverse an NxN matrix according to the JPEG "zigzag" scan pattern. The following is an example traversal over an 8x8 matrix (referenced from here:) Examples (The middle matrix is not part of the input or output, just a representation of the NxN matrix the input represents.) 1 2 3 (Input) 3 --> 4 5 6 --> 1 2 4 7 5 3 6 8 9 (Output) 7 8 9 1 2 3 4 (Input) 4 --> 5 6 7 8 --> 1 2 5 9 6 3 4 7 10 13 14 11 8 12 15 16 (Output) 9 10 11 12 13 14 15 16 Notes: The resulting array's base should be appropriate for your language (e.g., Matlab arrays are 1-based, C++ arrays are 0-based). This is related to this question.

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• Wrong getBounds() on LineScaleMode.NONE

  - by ghalex

  I have write a simple example that adds a canvas and draw a rectangle with stroke size 20 scale mode none. The problem is that if I call getBounds() first time I will get a correct result but after I call scale(); the getBounds() function will give me a wrong result. It will take in cosideration the stroke but stroke has scalemode to none and on the screen nothing happens but in the result I will have a x value smaller. Can sombody tell me how can I fix this ? protected var display :Canvas; protected function addCanvas():void { display = new Canvas(); display.x = display.y = 50; display.width = 100; display.height = 100; display.graphics.clear(); display.graphics.lineStyle( 20, 0x000000, 0.5, true, LineScaleMode.NONE ); display.graphics.beginFill( 0xff0000, 1 ); display.graphics.drawRect(0, 0, 100, 100); display.graphics.endFill(); area.addChild( display ); traceBounce(); } protected function scale():void { var m :Matrix = display.transform.matrix; var apply :Matrix = new Matrix(); apply.scale( 2, 1 ); apply.concat( m ); display.transform.matrix = apply; traceBounce(); } protected function traceBounce():void { trace( display.getBounds( this ) ); }

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• multidimensional array

  - by Codenotguru

  how to transpose a 2D matrix in place?

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• Flash "visible" issue

  - by justkevin

  I'm writing a tool in Flex that lets me design composite sprites using layered bitmaps and then "bake" them into a low overhead single bitmapData. I've discovered a strange behavior I can't explain: toggling the "visible" property of my layers works twice for each layer (i.e., I can turn it off, then on again) and then never again for that layer-- the layer stays visible from that point on. If I override "set visible" on the layer as such: override public function set visible(value:Boolean):void { if(value == false) this.alpha = 0; else {this.alpha = 1;} } The problem goes away and I can toggle "visibility" as much as I want. Any ideas what might be causing this? Edit: Here is the code that makes the call: private function onVisibleChange():void { _layer.visible = layerVisible.selected; changed(); } The changed() method "bakes" the bitmap: public function getBaked():BitmapData { var w:int = _composite.width + (_atmosphereOuterBlur * 2); var h:int = _composite.height + (_atmosphereOuterBlur * 2); var bmpData:BitmapData = new BitmapData(w,h,true,0x00000000); var matrix:Matrix = new Matrix(); var bounds:Rectangle = this.getBounds(this); matrix.translate(w/2,h/2); bmpData.draw(this,matrix,null,null,new Rectangle(0,0,w,h),true); return bmpData; } Incidentally, while the layer is still visible, using the Flex debugger I can verify that the layer's visible value is "false".

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• Howto transpose multidimensional array in place

  - by Codenotguru

  how to transpose a 2D matrix in place?

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• Resize image while rotating image in android

  - by dhams

  Hi every one ,,m working with android project in which i want to rotate image along with touch to some fix pivot point ,,,i have completed all the things but i have facing one problem ,,,while m trying to rotate image the image bitmap is resize....i dont have any idea why it occur ....if somebody have den please give me idea to come over this problem.... my code is below ..... package com.demo.rotation; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Matrix; import android.os.Bundle; import android.util.Log; import android.view.MotionEvent; import android.view.View; import android.view.View.OnTouchListener; import android.widget.ImageView; import android.widget.ImageView.ScaleType; public class temp extends Activity{ ImageView img1; float startX; float startX2 ; Bitmap source; Bitmap bitmap1 = null; double r; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); img1 = (ImageView) findViewById(R.id.img1); img1.setOnTouchListener(img1TouchListener); bitmap1 = BitmapFactory.decodeResource(getResources(), R.drawable.orsl_circle_transparent); } private OnTouchListener img1TouchListener = new OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_MOVE: Log.d("MOVE", "1"); if(source!=null) r = Math.atan2(event.getX() - source.getWidth(), (source.getHeight() / 2) - event.getY()); Log.i("startX" + event.getX(), "startY" + event.getY()); rotate(r,bitmap1, img1); img1.setScaleType(ScaleType.CENTER); break; case MotionEvent.ACTION_DOWN: break; case MotionEvent.ACTION_UP: break; default : break; } return true; } }; private void rotate(double r , Bitmap currentBitmap ,ImageView imageView ) { int rotation = (int) Math.toDegrees(r); Matrix matrix = new Matrix(); matrix.setRotate(rotation, currentBitmap.getWidth()/2, currentBitmap.getHeight()/2); source = Bitmap.createBitmap(currentBitmap, 0, 0, currentBitmap.getWidth(), currentBitmap.getHeight(), matrix, false); imageView.setImageBitmap(source); Log.i("HIGHT OF CURRENT BITMAP", ""+source.getHeight()); } }

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• R library for discrete Markov chain simulation

  - by stevejb

  Hello, I am looking for something like the 'msm' package, but for discrete Markov chains. For example, if I had a transition matrix defined as such Pi <- matrix(c(1/3,1/3,1/3, 0,2/3,1/6, 2/3,0,1/2)) for states A,B,C. How can I simulate a Markov chain according to that transition matrix? Thanks,

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• pyplot: really slow creating heatmaps

  - by cvondrick

  I have a loop that executes the body about 200 times. In each loop iteration, it does a sophisticated calculation, and then as debugging, I wish to produce a heatmap of a NxM matrix. But, generating this heatmap is unbearably slow and significantly slow downs an already slow algorithm. My code is along the lines: import numpy import matplotlib.pyplot as plt for i in range(200): matrix = complex_calculation() plt.set_cmap("gray") plt.imshow(matrix) plt.savefig("frame{0}.png".format(i)) The matrix, from numpy, is not huge --- 300 x 600 of doubles. Even if I do not save the figure and instead update an on-screen plot, it's even slower. Surely I must be abusing pyplot. (Matlab can do this, no problem.) How do I speed this up?

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• What is the optimum way to secure a company wide wiki?

  - by Mark Robinson

  We have a wiki which is used by over half our company. Generally it has been very positively received. However, there is a concern over security - not letting confidential information fall into the wrong hands (i.e. competitors). The default answer is to create a complicated security matrix defining who can read what document (wiki page) based on who created it. Personally I think this mainly solves the wrong problem because it creates barriers within the company instead of a barrier to the external world. But some are concerned that people at a customer site might share information with a customer which then goes to the competitor. The administration of such a matrix is a nightmare because (1) the matrix is based on department and not projects (this is a matrix organisation), and (2) because in a wiki all pages are by definition dynamic so what is confidential today might not be confidential tomorrow (but the history is always readable!). Apart from the security matrix, we've considered restricting content on the wiki to non super secret stuff, but off course that needs to be monitored. Another solution (the current) is to monitor views and report anything suspicious (e.g. one person at a customer site having 2000 views in two days was reported). Again - this is not ideal because this does not directly imply a wrong motive. Does anyone have a better solution? How can a company wide wiki be made secure and yet keep its low threshold USP? BTW we use MediaWiki with Lockdown to exclude some administrative staff.

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• What is the best way to flag some elements in MATLAB? using NaN or Inf? or something else?

  - by Kamran Bigdely Shamloo

  As you may know, in many occasions, there is a need to flag some elements of a matrix. For example when we have weighted adjacency matrix, and our graph is not fully connected, we have to flag some elements to show that there is no edge between those nodes. The question is how to do that? Is it better to put NaN or Inf on that elements in the matrix? or something elese(such as -1)?

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• Calculating rotation and translation matrices between two odometry positions for monocular linear triangulation

  - by user1298891

  Recently I've been trying to implement a system to identify and triangulate the 3D position of an object in a robotic system. The general outline of the process goes as follows: Identify the object using SURF matching, from a set of "training" images to the actual live feed from the camera Move/rotate the robot a certain amount Identify the object using SURF again in this new view Now I have: a set of corresponding 2D points (same object from the two different views), two odometry locations (position + orientation), and camera intrinsics (focal length, principal point, etc.) since it's been calibrated beforehand, so I should be able to create the 2 projection matrices and triangulate using a basic linear triangulation method as in Hartley & Zissermann's book Multiple View Geometry, pg. 312. Solve the AX = 0 equation for each of the corresponding 2D points, then take the average In practice, the triangulation only works when there's almost no change in rotation; if the robot even rotates a slight bit while moving (due to e.g. wheel slippage) then the estimate is way off. This also applies for simulation. Since I can only post two hyperlinks, here's a link to a page with images from the simulation (on the map, the red square is simulated robot position and orientation, and the yellow square is estimated position of the object using linear triangulation.) So you can see that the estimate is thrown way off even by a little rotation, as in Position 2 on that page (that was 15 degrees; if I rotate it any more then the estimate is completely off the map), even in a simulated environment where a perfect calibration matrix is known. In a real environment when I actually move around with the robot, it's worse. There aren't any problems with obtaining point correspondences, nor with actually solving the AX = 0 equation once I compute the A matrix, so I figure it probably has to do with how I'm setting up the two camera projection matrices, specifically how I'm calculating the translation and rotation matrices from the position/orientation info I have relative to the world frame. How I'm doing that right now is: Rotation matrix is composed by creating a 1x3 matrix [0, (change in orientation angle), 0] and then converting that to a 3x3 one using OpenCV's Rodrigues function Translation matrix is composed by rotating the two points (start angle) degrees and then subtracting the final position from the initial position, in order to get the robot's straight and lateral movement relative to its starting orientation Which results in the first projection matrix being K [I | 0] and the second being K [R | T], with R and T calculated as described above. Is there anything I'm doing really wrong here? Or could it possibly be some other problem? Any help would be greatly appreciated.

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• Flex/Actionscript image display problem.

  - by IanH

  I'm trying to extend the Image class but hit a problem that I can't get past. I have a private image (img) that loads an image and a function that takes that image and copies it onto the parent. The debug function "copyit2" displays the image fine (so I know it's loaded OK). But the function "copyit" doesn't work - it just displays a white rectangle. I can't see how to make copyit work so that the original image is copied to the BitmapData and then subsequenty copied onto the parent? (The idea is to do some processing on the Bitmap data before it is displayed, although this isn't shown here to keep the example simple.) I suspect it is something to do with the security of loading images, but I'm loading it from the same server as the application is run from - so this shouldn't be a problem? Thanks for any help anyone can provide. Ian package zoomapackage { import flash.display.Bitmap; import flash.display.BitmapData; import flash.display.Sprite; import flash.events.MouseEvent; import flash.geom.Matrix; import flash.geom.Point; import flash.geom.Rectangle; import flash.net.*; import mx.controls.Image; import mx.events.FlexEvent; public dynamic class Zooma extends Image { private var img:Image; public function copyit():void { var imgObj:BitmapData = new BitmapData(img.content.width, img.content.height, false); imgObj.draw(img); var matrix:Matrix = new Matrix(); this.graphics.beginBitmapFill(imgObj, matrix, false,true); this.graphics.drawRect(0, 0, this.width , this.height); this.graphics.endFill(); } public function copyit2():void { this.source = img.source; } public function Zooma() { super(); img = new Image(); img.load("http://localhost/Koala.jpg"); } } }

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• Architecture Guidance for designing Workflow Foundation with WCF

  - by Matrix

  We are planning to use WF 3.5 with WCF 3.5 and Entity Framework 1.0 for the upcoming major project. I'm looking for guidance on the architecture side. This new application will be based on typical 3-tier architecture as depicted below: Presentation Tier: ASP.NET Web Forms 3.5 Business Tier: WF 3.5 + BLL's that expose the business logic through WCF service interfaces (using EF for Data Access) Data Tier: SQL Server 2000 Here are the questions: Though the Workflow Foundation has Workflow Services, where we can map the WCF service contracts to a workflow, is this the right way to design the applications? Is EF 1.0 business entities can be used in n-tier apps without sacrificing the tracking changes in the entities? Is there a sample reference application available to look? Thanks.

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• XNA 2d camera with arbitrary zoom center

  - by blooop

  I have a working 2D camera in XNA with these guts: ms = Mouse.GetState(); msv = new Vector2(ms.X, ms.Y); //screenspace mouse vecor pos = new Vector2(0, 0); //camera center of view zoom_center = cursor; //I would like to be able to define the zoom center in world coords offset = new Vector2(scrnwidth / 2, scrnheight / 2); transmatrix = Matrix.CreateTranslation(-pos.X, -pos.Y, 0) * Matrix.CreateScale(scale, scale, 1) * Matrix.CreateTranslation(offset.X, offset.Y, 0); inverse = Matrix.Invert(transmatrix); cursor = Vector2.Transform(msv, inverse); //the mouse position in world coords I can move the camera position around and change the zoom level (with other code that I have not pasted here for brevity). The camera always zooms around the center of the screen, but I would like to be able to zoom about an arbitrary zoom point (the cursor in this case), like the indie game dyson http://www.youtube.com/watch?v=YiwjjCMqnpg&feature=player_detailpage#t=144s I have tried all the combinations that make sense to me, but am completely stuck.

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• roundoff double values in Java

  - by S.PRATHIBA

  Hi all, I have a matrix.I found the 10th power of matrix using Java.After finding the 10th power,I need to round off the double values to 3 decimal places.Please help me to round off the double values in the matrix to 3 decimal places.

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• Inline function and calling cost in C

  - by Eonil

  I'm making a vector/matrix library. (GCC, ARM NEON, iPhone) typedef struct{ float v[4]; } Vector; typedef struct{ Vector v[4]; } Matrix; I passed struct data as pointer to avoid performance degrade from data copying when calling function. So I thought designed function like this: void makeTranslation(const Vector* factor, Matrix* restrict result); But, if function is inline, is there any reason to pass values as pointer for performance? Do those variables copied too? How about register and caches? inline Matrix makeTranslation(Vector factor) __attribute__ ((always_inline)); How do you think about calling costs of each cases?

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• in R, question about generate table

  - by alex

  a = matrix(1:25,5,5) B = capture.output(for (X in 1:5){ A = c(min(a[,X]),quantile(a[,X],0.25),median(a[,X]),quantile(a[,X],0.75),max(a[,X]),mean(a[,X]),sd(a[,X])/m^(1/2),var(a[,X])) cat(A,"\n") }) matrix(B,8,5) what i was trying to do is to generate a table which each column has those element in A and in that order. i try to use the matrix, but seems like it dont reli work here...can anyone help 1 2 3 4 5 min 1st quartile median SEM VAR THIS IS WHAT I WANT THE TABLE LOOKS LIKE ..

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• developing a chat website

  - by akshay

  I want to develop a anonimous chat website like omgele.com.I know that this website is devloped in python using twisted matrix framework.Using twsited matrix its easy to devlop such website. But i am very comfortable in java and have 1 yr expericne in it.and dont know python. What shold i do? Should i start learning python to take advanctage of the twiste matrix framework?? OR Should i develop it in java?If so which framework you would suggest to do so?

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• Basic FreeMat/MATLAB syntax - dimension error

  - by 0x90

  I am using FreeMat, and I have an RGB picture which is a 3D matrix contains the columns and rows of the pictures and the RGB values for each pixel. Since there is not an intrinsic function to convert RGB picture to YIQ, I have implement one. I came up with this code: Assume I have a 3D array, image_rgb: matrix = [0.299 0.587 0.114; 0.596 -0.274 -0.322; 0.211 -0.523 0.312]; row = 1:length(image_rgb(:,1,1)); col = 1:length(image_rgb(1,:,1)); p = image_rgb(row,col,:); %Here I have the problem mage_yiq(row,col,:) = matrix*image_rgb(row,col,:); max_y = max (max(image_yiq(:,:,1))); max_i = max (max(image_yiq(:,:,2))); max_q = max (max(image_yiq(:,:,3))); %Renormalize the image again after the multipication % to [0,1]. image_yiq(:,:,1) = image_yiq(:,:,1)/max_y; image_yiq(:,:,2) = image_yiq(:,:,2)/max_i; image_yiq(:,:,3) = image_yiq(:,:,3)/max_q; I can't understand why the matrix multiplication fails. I want the code to be nice and not just to, multiply the matrix by hand...

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• trouble calculating offset index into 3D array

  - by Derek

  Hello, I am writing a CUDA kernel to create a 3x3 covariance matrix for each location in the rows*cols main matrix. So that 3D matrix is rows*cols*9 in size, which i allocated in a single malloc accordingly. I need to access this in a single index value the 9 values of the 3x3 covariance matrix get their values set according to the appropriate row r and column c from some other 2D arrays. In other words - I need to calculate the appropriate index to access the 9 elements of the 3x3 covariance matrix, as well as the row and column offset of the 2D matrices that are inputs to the value, as well as the appropriate index for the storage array. i have tried to simplify it down to the following: //I am calling this kernel with 1D blocks who are 512 cols x 1row. TILE_WIDTH=512 int bx = blockIdx.x; int by = blockIdx.y; int tx = threadIdx.x; int ty = threadIdx.y; int r = by + ty; int c = bx*TILE_WIDTH + tx; int offset = r*cols+c; int ndx = r*cols*rows + c*cols; if((r < rows) && (c < cols)){ //this IF statement is trying to avoid the case where a threadblock went bigger than my original array..not sure if correct d_cov[ndx + 0] = otherArray[offset]; d_cov[ndx + 1] = otherArray[offset] d_cov[ndx + 2] = otherArray[offset] d_cov[ndx + 3] = otherArray[offset] d_cov[ndx + 4] = otherArray[offset] d_cov[ndx + 5] = otherArray[offset] d_cov[ndx + 6] = otherArray[offset] d_cov[ndx + 7] = otherArray[offset] d_cov[ndx + 8] = otherArray[offset] } When I check this array with the values calculated on the CPU, which loops over i=rows, j=cols, k = 1..9 The results do not match up. in other words d_cov[i*rows*cols + j*cols + k] != correctAnswer[i][j][k] Can anyone give me any tips on how to sovle this problem? Is it an indexing problem, or some other logic error?

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• Optimization Techniques in Python

  - by fear-matrix

  Recently i have developed a billing application for my company with Python/Django. For few months everything was fine but now i am observing that the performance is dropping because of more and more users using that applications. Now the problem is that the application is now very critical for the finance team. Now the finance team are after my life for sorting out the performance issue. I have no other option but to find a way to increase the performance of the billing application. So do you guys know any performance optimization techniques in python that will really help me with the scalability issue

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