search for: convexity

..., URL = "http://www.amstat.org/publications/jcgs/abstracts98/jongbloed.html", acknowledgement = ack-nhfb, } ------ I know about Roger Koenker and Pin Ng's very interesting "nprq" package (and its earlier version "cobs") where one can fit splines with convexity constraints. At the moment however, we are specifically interested in the ICM algorithm for convex nonparametric regression. Thank you for pointers in advance. Martin Maechler, ETH Zurich

Dear UseRs, I would like to know which function is the most efficient in finding convex hull of points in 3(or 2)-dimensional case? Functions for finding convex hull is the following: convex.hull (tripack), chull (grDevices), in.chull (sgeostat), convhulln (geometry), convexhull.xy (spatstat), calcConvexHull (PBSmapping). I also would like to know if there is a function that can be used

Recently, a package for convex optimization was announced for Python, based upon the LP solver GLPK, the SDP solver in DSDP5, and the LP and QP solvers in MOSEK. I'm aware GLPK is available for R, but wondered if anyone had good packages for convex optimization along these lines for R. TIA.

Dear list, Does anyone have a suggestion (or better still) code for sampling from the uniform distribution over the convex hull of a set of points? Many thanks and best wishes, Ranjan

Dear R gurus and users, I seem to have problem finding the right tool for plotting convex hulls over 2D plots, after a cluster analysis. In fact I would like to draw a convex hull in 2D for a generic group of points. I found a "convhulln", but this doesn't seem to give me a convex hull. Here is what I do: > library(mvtnorm) > Mean <- c(2,1) > Sigma <-

Dear List Members, I'm presently carrying out morphological analysis of a data set of neuronal structures. These are essentially 3D binary trees. In due course I will be trying to use discriminant analysis or other methods to classify these neurons based on morphological variables such as total tree length, segment number etc. I would like to calculate a 3D convex hull for a set of X,Y,Z

Hi my R buddies, I'm trying to solve a specific group of convex optimization in R. The admissible region is the inside and surface of a multi-dimensional eclipse area and the goal function is the sum of absolution values of the variables. Could any one please tell me whether there's a package in R to do this? Thank you very much, Best wishes, -- ??? Hesen Peng

Does anyone know of a R package that will determine the convex hull of a high-dimensional dataset (say 4-10 dimensions). I know chull works for 2D data. I'm neophyte to R and convex hulls so please keep it simple. Many thanks Ben -- Ben Stapley. Biomolecular Sciences, UMIST, PO Box 88, Manchester M60 1QD. Tel 0161 200 5818 Fax 0161 236 0409

Hi there, I have been using the Tps function (within the Fields package) for a while now to interpolate different sedimentary units. Due to the method of formation of the units I know that at some edges the thickness of the unit decreases to zero. I was wondering if there was someway to specify that the interpolation only occurs within the convex hull of the data, outside of which the the values

I am modeling a trend surface using trmat and want to trim the resulting matrix to the area enclosed by my real data (i.e., remove all the extrapolated areas). I was using chull and in.chull to calculate the convex hull and change all the other values created by trmat to NA. However, my real data has portions that are slightly concave so chull would give me slivers that are extrapolations from

...of CVXR which implements Disciplined Convex Programming (DCP) in R on CRAN. Like CVXPY in Python, CVXR provides a domain specific language for formulating convexoptimization problems in a natural way following mathematical convention and DCP rules. The system analyzes the problem, verifies its convexity, converts it into a canonical form, and hands it off to an appropriate solver to obtain the solution. Applications of convex programming are described in a paper available at https://stanford.edu/~boyd/papers/pdf/cvxr_paper.pdf <https://stanford.edu/%7Eboyd/papers/pdf/cvxr_paper.pdf> . A...

I am running the following code (testing the use of the simplex function to determine if a point is in the convex hull of another set of points or not): >a <- c(0, 0) >A3 <-matrix(c(1,2,3,4,1,1), ncol = 2, byrow = T) >b3 <-c(1.5, 3.5, 1) >simplex(a = a, A3 = A3, b3 = b3) and the following error message appears: Error in simplex1(out1$a[1:(n + m1 + m2)], out1$A[, 1:(n + m1

Ranjan Maitra writes: > Does anyone have a suggestion (or better still) code for sampling > from the uniform distribution over the convex hull of a set of > points? This is implemented in library 'spatstat'. If x and y are vectors of coordinates of your initial set of points, library(spatstat) W <- convexhull.xy(x, y) P <- runifpoint(42, W) will compute

Hi everyone, I wonder if there is a code in r that can generate a 3d convex hull from a data-frame containing 3 columns and then use another database with the same three columns and for each row determine if the xyz point is inside or not the convex hull generated with the first database? The package geometry allows to calculate a hull and it's volume. I was planning to calculate the volume

...of CVXR which implements Disciplined Convex Programming (DCP) in R on CRAN. Like CVXPY in Python, CVXR provides a domain specific language for formulating convexoptimization problems in a natural way following mathematical convention and DCP rules. The system analyzes the problem, verifies its convexity, converts it into a canonical form, and hands it off to an appropriate solver to obtain the solution. Applications of convex programming are described in a paper available at https://stanford.edu/~boyd/papers/pdf/cvxr_paper.pdf <https://stanford.edu/%7Eboyd/papers/pdf/cvxr_paper.pdf> . A...

Does anybody know if there are functions to: 1. Define a convex hull on a space with more than 2 dimensions? chull just works for a plane. 2. Numerically select elements within a given complex hull. Thanks! Dr. Agustin Lobo Instituto de Ciencias de la Tierra (CSIC) Lluis Sole Sabaris s/n 08028 Barcelona SPAIN tel 34 93409 5410 fax 34 93411 0012 alobo at ija.csic.es

Hello, I am trying to draw a convex-polygon (envelope) connecting the outer points (of a particular class) in a scatter plot [which I want to do to illustrate the range of a particular type of samples in an ordination plot]. Is there any function to plot this kind of polygon? Kind regards Zlatko Petrin

Hi, I seek to identify those points in/outside a multidimensional convex hull (geometry::convhulln). Any suggestions? Background just in case I'm going down a really wrong road: Given an observed data set with one dependent/observed variable (Y) and multiple (3 to 10) independent/design variables (X1, X2, ...) I want to increase the number of points by interpolating. I'm using

Hi everyone, Using a simulation, I have to find what are the probabilities that, in a square region, the convex hull is a triangle, using the "chull" function. However, I have a hard time with the chull function, i did not see many examples in which the chull function is used. I searched a long time on google, but I did not find nothing. So, if anyone can help, Thanks!

Full_Name: Jonathan Lees Version: 2.0.1 OS: linux-gnu Submission from: (NULL) (152.2.75.65) there is a problem with calculating the convex hull in 2-D interpolation using the codes interp fromt eh akima package: x =c(0.6505304, -1.1821562, -0.2600792, 0.7913716) y = c(1.0424226, 0.1754048, -1.4523334, 0.2349112) z = c(0.000, 3.042, 0.370, 0.122) EX = seq(from=min(x), to=max(x),