I have a class called forest and a property called fixedPositions that stores 100 points (x,y) and they are stored 250x2 (rows x columns) in MatLab. When I select 'fixedPositions', I can click scatter and it will plot the points. Now, I want to rotate the plotted points and I have a rotation matrix that will allow me to do that. The...
Hi, I would like to know if anyone has info or experience on how to do something which sounds simple but doesn't look like it when trying to program it. The idea is : give a string containing an equation, such as : "2*x = 10" for example (this is simple, but it could get very complex, such as sqrt(54)*35=x^2; and so on....) and the progr...
Doing some 3D stuff in wpf- want to use a simpler test to see if everything is working (before moving to curves). The basic question is given two points x1,y1,z1 and x2,y2,z2 I have calculated the distance between the points. But how to find the coordinates of another point (x3,y3,z3) that lies on that line at some distance? I.e. if m...
How can I perform vector calculations in lisp, such as magnitude of a vector, norm of a vector, distance (between two points), dot product, cross product, etc. Thanks. ...
greetings, I'm not sure if this is a dumb question or not. Lets say I have 3 numpy arrays, A1,A2,A3, and 3 floats, c1,c2,c3 and I'd like to evaluate B = A1*c1+ A2*c2+ A3*c3 will numpy compute this as for example, E1 = A1*c1 E2 = A2*c2 E3 = A3*c3 D1 = E1+E2 B = D1+E3 or is it more clever than that? In c++ I had a neat way to a...
Aye it's been done a million times before, but damnit I want to do it again. I'm writing a simple Matrix Library for C++ with the intention of doing it right. I've come across something that's fairly obvious in mathematics, but not so obvious to a strongly typed system -- the fact that a 1x1 matrix is just a number. To avoid this, I s...
I'm attempting to solve a set of equations of the form Ax = 0. A is known 6x6 matrix and I've written the below code using SVD to get the vector x which works to a certain extent. The answer is approximately correct but not good enough to be useful to me, how can I improve the precision of the calculation? Lowering eps below 1.e-4 causes...
This great SO answer points to a good sparse solver for Ax=b, but I've got constraints on x such that each element in x is >=0 an <=N. Also, A is huge (around 2e6x2e6) but very sparse with <=4 elements per row. Any ideas/recommendations? I'm looking for something like MATLAB's lsqlin but with huge sparse matrices. I'm essentially try...
R has a qr() function, which performs QR decomposition using either LINPACK or LAPACK (in my experience, the latter is 5% faster). The main object returned is a matrix "qr" that contains in the upper triangular matrix R (i.e. R=qr[upper.tri(qr)]). So far so good. The lower triangular part of qr contains Q "in compact form". One can extra...
Hi everyone, I've been working on a Flash game that involves an isometric space. I've been using as3isolib for a while now, and I'm less than impressed with how easy it is to use. Whether I'm approaching it the wrong way or it's just not that great to use is a question for another post. Anyways, I've been thinking of a different way ...
I use numpy for numerical linear algebra. I suspect that I can get much better performance if I make small modifications in how I carry out certain computations so that they are more memory efficient, for example. I was wondering if there is any form of instrumentation available in python to detect cache and TLB misses. There is a very ...
Is there a function in R that produces the reduced row echelon form of a matrix?. This reference says there isn't. Do you agree? ...
How do I do a perspective view transformation in Java? As I understand it there is some magical 4 dimensional matrix I can use which will determine the FOV, Aspect Ratio, and Near and Far viewing distances, but I don't know how to create that matrix. I'm able to implement a "PerspectiveTransform" in Java, but I see no effect when using ...
A linear algebra question; Given a k-variate normed vector u (i.e. u : ||u||_2=1) how do you construct \Gamma_u, any arbitrary k*(k-1) matrix of unit vectors such that (u,\Gamma_u) forms an orthogonal basis ? I mean: from a computationnal stand point of view: what algorithm do you use to construct such matrices ? Thanks in advance,...
I am currently working on a C++ sparse matrix/math/iterative solver library, for a simulation tool I manage. I would have preferred to use an existing package, however, after extensive investigation, none were found that were appropriate for our simulator (we looked at flens, it++, PetSC, eigen, and several others). The good news is my...
I am trying to work out if I can parallelise the training aspect of a machine learning algorithm. The computationally expensive part of the training involves Cholesky decomposing a positive-definite matrix (covariance matrix). I'll try and frame the question purely in terms of the matrix algebra. Let me know if you need any more info. L...
i'd like to do large-scale regression (linear/logistic) in R with many (e.g. 100k) features, where each example is relatively sparse in the feature space---e.g., ~1k non-zero features per example. it seems like the SparseM package slm should do this, but i'm having difficulty converting from the sparseMatrix format to a slm-friendly for...
I have scene composed of one arbitrary quadrilateral. I need to be able to transform that quadrilateral into a rect. Each quad is in 2d coordinates, so they have 4 vertex (x_i, y_i). The transformation need to have an inverse because the idea is to go back to the original quad after manipulating the rectangle. What would be the easiest...
Given a matrix A (not neccessarily square) with independent columns, I was able to apply Gram-Schmidt iteration and produce an orthonormal basis for its columnspace (in the form of an orthogonal matrix Q) using Matlab's function qr A=[1,1;1,0;1,2] [Q,R] = qr(A) and then >> Q(:,1:size(A,2)) ans = -0.577350269189626 -0.000000000000...
Method lu of package Matrix works fine for square matrices. However, I can't see why there is that square restriction. How can I perform LU decomposition on a rectangular matrix? ...