# Questions tagged [matrix]

16270 questions

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### Trading in precision for better recall in Keras classification neural net

There's always a tradeoff between precision and recall. I'm dealing with a multi-class problem, where for some classes I have perfect precision but really low recall.
Since for my problem false positives are less of an issue than missing true positives, I want reduce precision in favor of increasin...

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1

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### java.lang.IllegalArgumentException: Matrix inner dimensions must agree

Here is my code:
package algorithms;
import Jama.Matrix;
import java.io.File;
import java.util.Arrays;
public class ThetaGetter {
//First column is one, second is price and third is BHK
private static double[][] variables = {
{1,1130,2},
{1,1100,2},
{1,2055,3},
{1,1047,2},
{1,1927,3},
{1,2667,3},
{1...

1

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1

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784

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### Create clusters using correlation matrix in Python

all, I have a correlation matrix of 21 industry sectors. Now I want to split these 21 sectors into 4 or 5 groups, with sectors of similar behaviors grouped together.
Can experts shed me some lights on how to do this in Python please? Thanks much in advance!

1

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1

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154

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### How to create a video from images?

I have an algorithm, which after each iteration creates a matrix. After some operations on matrix it is plotted to the user. if I run program 6 times I will get:
My goal is to changing image dynamically, like a movie.
I have no idea from which side to start. I found some ways of creating video from...

0

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0

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5

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### Range minimum query of special binary array

Let A be a binary array (that is, it contains only -1s and 1s), but with a special rule: the true value of A[i] is A[0] + ... + A[i].
Suppose A = {1,1,-1,-1}, than the array of real values should be {1,2,1,0}.
How can I retrieve the index of a Range Minimum Query on A without preprocessing the real...

1

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1

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51

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### Understanding the OpenGL projection matrix

I've been writing a program to display 3d models using OpenGL and until now I've used orthographic projection, but I want to switch to a perspective projection so that as the camera goes toward the model it appears to get larger. I understand that I have to multiply three matrices (model, view, and...

1

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2

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44

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### Summing selected elements of a matrix in Python

I have a [n x n] matrix containing values belonging to different groups, and a [1 x n] vector defining to which group each element belongs.
(n usually ~1E4, in this example n=4)
I want to calculate a matrix obtained by summing together all the elements belonging to the same group.
I use np.where() t...

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2

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34

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### Splitting a matrix row based

I have a question with dividing matrixes.
I have data of 100 rows and 1024 columns. I want to split that matrix into 2 sub matrices such that 8 rows to matrix 1 and 2 rows to matrix 2
first matrix will be formed
r1
r2
r3
r4
r5
r6
r7
r8
r11
r12
r13
...
...
and the second matrix will be formed with
r...

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3

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31

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### Given an N-side square matrix, is there a way to find the ring value of a cell without using loops or if conditions?

For instance, imagine you have a 6-side square matrix.
These are the cells cartesian indices:
(0,0) (0,1) (0,2) (0,3) (0,4) (0,5)
(1,0) (1,1) (1,2) (1,3) (1,4) (1,5)
(2,0) (2,1) (2,2) (2,3) (2,4) (2,5)
(3,0) (3,1) (3,2) (3,3) (3,4) (3,5)
(4,0) (4,1) (4,2) (4,3) (4,4) (4,5)
(5,0) (5,1) (5,2) (5,3) (5...

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2

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### Turning a presence-absence matrix into a single variable per row in R

I have a presence absence matrix (comprised of 1s and 0s) for each individual ID. It is based on mark recapture data. Each column represents a sampling date. As a data frame, it looks like this (first 3 rows):
ID X X.1 X.2 X.3 X.4 X.5 Sex
2014-001 0 0 1 0 1 0 F
2014-002 0 0...

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### Operations in a matrix with its (i,j) values with no for or while loops

I need to write a function in R that receives as inputs the number of rows (r) and the number of columns (c) and generates and output matrix V, where V_(i,j) = r^(abs(i-j)) and r = 2. This function must not have for nor while loops.
I just don't know how to access every (i,j) and compute de differen...

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1

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28

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### How to pretty print a matrix in Octave?

I want to create a pretty printed table from a matrix (or column vector).
For Matlab there are several available functions that can do this (such as printmat, array2table, and table), but for Octave I cannot find any.
So instead of:
>> a = rand(3,2)*10;
>> round(a)
ans =
2 10
1 3
2 1
I woul...

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2

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14

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### Manually multiplying two matrices in R

I am using R v 3.0.0 (2013-04-03) and RStudio v 1.1.463 under Win-7 64-bit.
In the following source code:
# Problem 1 - Matrix powers in R
#
# R does not have a built-in command for taking matrix powers.
# Write a function matrixpower with two arguments mat and k that
# will take integer powers k...

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2

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### i need to find the first negative number in each column of a matrix

Hello i need to find the position of first negative number for each row vector in a matrix
i've tried with match and apply but it ony shows the first
z

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2

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2.2k

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### Generate pixel matrices from characters in string [duplicate]

This question already has an answer here:
How to convert from alphabets to pixels
2 answers
I'm in the process of writing a library that will print scrolling text across an LED matrix hooked up to a Raspberry Pi.
I would like a function that takes a character, height and width and produces a matrix...

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2

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1.5k

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### OpenCV mean function crashes with mask created from OpenCV threshold function?

I'm very new to OpenCV, so I guess I'm making some silly mistake.
First I'm creating an empty cv::mat matrix, mask, of CV_8U type and filling it with zeros. Then I'm filling the matrix with either 0's or 255's by checking the values in CV_32FC1 type cv::mat matrix croppedDifferenceImage by the use...

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### List of all diagonals in a matrix without using numpy - Python 3

Let's say I got the following matrix:
[[5,4,3,2], [8,7,6,5], [4,3,2,0]]
I want to create 2 seperate functions that create a list of all diagonals from right to left, and from left to right without using the numpy module!
for e.x:
[[4], [8,3], [5,7,2], [4,6,0], [3,5], [2]] # these are the right to...

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1

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### How can I convert a column vector to the diagonal of a matrix? [duplicate]

This question already has an answer here:
How do I convert a n*1 matrix to a n*n diagonal matrix
3 answers
I have a column vector that I would like to convert to a diagonal matrix.
That is I have the vector v = (1,2,3) and want to turn it into:
[1, 0, 0]
[0, 2, 0]
[0, 0, 3]
How can I do this in Exc...

1

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2

answer

420

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### How to calculate diagonal of a matrix product in Tensorflow?

I have two matrices A and B of shape (M, N) with very large M and small N.
I would like to multiply them and then take diagonal of a result:
C = tf.matmul(A, B)
D = tf.diag_part(C)
Unfortunately, this requires of creating of very big (M, M) matrix, which can't fit into memory.
But most of this data...

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1

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10.8k

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### confusionMatrix for logistic regression in R

I want to calculate two confusion matrix for my logistic regression using my training data and my testing data:
logitMod = 0.5,
train$LoanStatus_B == 1))
And the the code below works well for my training set.
However, when i use the test set:
confusionMatrix(table(predict(logitMod, type='response')...

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2

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143

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### Tabulate a combined matrix of coefficients / t-statistics and export in LaTeX

I have many regressions (one per year, over fifteen years) for four outcome variables.
I have created two 15x4 matrices: one with the coefficients and one with the t-statistics. I am stuck now that I want to tabulate them in the classic way, each row having the coefficients for each model and under...

1

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3

answer

113

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### Construct an assignment matrix - Python

I have two lists of element
a = [1,2,3,2,3,1,1,1,1,1]
b = [3,1,2,1,2,3,3,3,3,3]
and I am trying to uniquely match the element from a to b, my expected result is like this:
1: 3
2: 1
3: 2
So I tried to construct an assignment matrix and then use scipy.linear_sum_assignment
a = [1,2,3,2,3,1,1,1,1,1]
b...

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3

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70

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### How to create matrix in python of repeating number?

I want to:
Create a vector list from 0 to 4, i.e. [0, 1, 2, 3, 4] and from that
Create a matrix containing a 'tiered list' from 0 to 4, 3 times over, once for each dimension. The matrix has 4^3 = 64 rows, so for example
T = [0 0 0
0 0 1
0 0 2
0 0 3
0 0 4
0 1 0
0 1 1
0 1 2
0 1 3...

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### producing a full adjacency matrix from partial information

I have a matrix that contains all the info necessary to construct 5x5 adjacency matrices. Each row represents one matrix:
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 1 1 1 1 1 1 0 1 0
[2,] 0 0 0 1 1 1 1 0 1 0
...
I want to c...

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1

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35

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### Why matrix to raster shows up rotated?

I am trying to convert a matrix (myMat) to raster data (myRas); however, I am not sure why this rotates all of a sudden. This can be easily fixed by 90-degree rotation using t() but, I will be grateful if someone explains why this unwanted rotation happens all the time?! and if there is a way to pre...

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3

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42

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### Add number to all negative values in a 4D matrix

I have a matrix DirModel of dimension 2x2x29x1739. I want to add 360 to all negative values in this matrix, but the code I use doesn't keep up the dimensions of this matrix, it makes it into an array:
Neg=DirModel

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3

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61

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### Find no of possible formations of explosive mines in a 2D matrix where some cells contain info about even/odd mines are adjacent to them

I am trying to make game involving 2D grid where given some hints a player can avoid cells containing explosive mines. I have come upon a particular scenario where given certain hints, i want to know how many formations of mines are possible.
Let there be a 2D matrix. Each cell may be empty or may c...

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27

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### Extract square matrices from a Nx2 matrix

I'm working on matlab 2014, I have a matrix 5124x2 and I want to extract all the 2562 square matrices.
I found that the unique solution is to use mat2Cell, but it doesn't work for me. I don't really need a cell array at the end, what I want is just all the square matrices
%example of data
A = rand(5...

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### How to plot heatmap using 2 matrix in r

I am trying to create a heatmap, but am confused as to how to. Here are the dataframes.
Ticker

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3

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87

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### How to save a matrix in C++ in a non-linear way

I have to program an optimized multi-thread implementation of the Levenshtein distance problem. It can be computed using dynamic programming with a matrix, the wikipedia page on Levenshtein distance covers that well enough.
Now, I can compute diagonal elements concurrently. That is all alright.
My...

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1

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33

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### Margrittr pipe with matrix operations in R

I'm working on some functions that take a matrix as input and provide a matrix as output. Is it possible to use the magrittr pipe with matrices without using the . placeholder? Ideally, I'd like these functions to be piped into each other like a dplyr chain. The issue is that I'm constantly forgetti...

1

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1

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74

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### C - Depth first search in adjacency matrix using recursion

I have a recursion problem I would like to solve using recursion.
For example, given this adjacency matrix AdjMat:
0 1 2 3
0 0 1 0 0
1 1 0 1 0
2 0 1 0 1
3 0 0 1 0
Say I would like to look at column 0 and all of its neighbors, and its neighbors' neighbors (distance of 2), and store all of the row in...

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### Creating an adjacency matrix from a cell array

I'm going to create an adjacency matrix from a cell array, but faced two main problems:
I don't know how to access to cell array's elements; so an adhoc method was used.
(and the most important) The code produces an error and the partial result is also a weird one!
The cell array is as the following...

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### Calculate Edit Distance between two strings in Python

I want to compute the edit distance matrix between two strings, at the character level.
Here is my function:
def editDistance(r, h):
'''
This function is to calculate the edit distance of reference sentence and the hypothesis sentence.
Main algorithm used is dynamic programming.
Attributes:
r -> the...

1

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0

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123

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### Error in colnames

Could anyone help me with some little problem?
When I plot the frontier I get the following message: 'Error in colnames

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100

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### Solving an overdetermined sparse linear system produces high error solution

My Code
So I have written an algorithm which iteratively solves a sparse overdetermined linear system. That means my code looks like this:
construct_A_matrix();
construct_B_matrix();
while(someCondition){
x=solveSystem(A,B) //solve Ax=B. This system is overdetermined
//since A has more rows than co...

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0

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### Matrix operations on labeled arrays

I have a system with a linearised set of equations, such that the time-update operation can be performed by a matrix multiplication, y' = Ay, but I would also like to be able to index y using the names of the state variables, e.g. y['vel']. Is there a way to index in this way without losing the abil...

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382

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### How to save the false positive and false negative of confusion matrix in image classification by using SVM?

I have successfully classified two classes of image using support vector machine and correctly calculated the confusion matrix. Here is my codes:
import sklearn
from sklearn import metrics
from sklearn import svm
from sklearn.svm import SVC
from sklearn.metrics import accuracy_score, f1_score, preci...

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1

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67

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### Solve a redundant system of linear equations in R

I have a noninvertible matrix A and a vector b for which I believe there is a solution x to Ax = b. I would like to find an example of such x. When I try solve(A,b) in R it produces an error because A is singular. Is there any way to make R give me a random solution?

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### Vector2.Transform(Vector2, Matrix) returns {X:n. def. Y:n. def.}

I'm trying to convert a Vector2 screen position to a world position. I've found this nice method in another Question:
public Vector2 ScreenToWorld(Vector2 onScreen)
{
var matrix = Matrix.Invert(World.Camera.CurrentTransformation);
return Vector2.Transform(onScreen, matrix);
}
But when I use this wit...