smooth.FEM.density: Compute a smooth FEM density surface of a triangulated...

In SpatialfdaR: Spatial Functional Data Analysis

Compute a smooth FEM density surface of a triangulated region.

Description

A spatial density defined over a region with complicated a boundary that is defined by a triangulation is estimated. The basis functions are linear finite elements (FEM) defined at each vertex. The data are the spatial coordinates of a sample of a defined spatial event. The density surface is the logarithm of the density, and the smoothness of the log surface is controlled by a smoothing parameter lambda multiplying the stiffness matrix.

Usage

smooth.FEM.density(obspts, cvec, FEMbasis, K1=NULL, lambda=0,
                 conv=1e-4, iterlim=50, dbglev=FALSE)

Arguments

obspts	A two-column matrix with each row corresponding to a location within a two-dimensional region bounded by line segments and containing a triangular mesh.
cvec	A matrix each column of which contains the coefficients for an FEM basis function expansion of a surface. The number of coefficients equals the number of vertices in the triangulation, also called the nodes of the FEM expansion.
FEMbasis	This argument provides the FEM basis (class basisfd), and may be in the form of an FEM basis object, an FEM function object (class fd), or an FEM functional parameter object (class fdPar.
K1	The stiffness matrix associated with the triangulation. It is computed using function stiff.FEM.
lambda	A non-negative real number controlling the smoothness of the surface by a roughness penalty consisting of lambda.
conv	The convergence criterion using the function value.
iterlim	The maximum number of permitted iterations.
dbglev	print debugging output.

Details

The penalized log likelihood of a density surface is minimized with respect to the coefficient vector. with the initial value in cvec. The spatial event locations are in the two-column matrix pts. The FEM basis object is extracted from IntensityfdPar, which may also be an FEM functional data object or an FEM basis object. The roughness penalty, if required, is the stiff matrix K1 multiplied by the roughness parameter lambda.

Value

cvec:	The final coefficient vector or matrix.
Intensityfd:	An FEM functional data object for the log density.
Flist:	A list object with F the final penalized log likelihood value, grad the final gradient and norm the final norm of the gradient.
iterhist:	A matrix with three columns displaying the iteration number, the function value and the norm of the gradient vector for the initial iteration and each subsequent iteration.

Author(s)

Jim Ramsay

References

Sangalli, Laura M., Ramsay, James O., Ramsay, Timothy O. (2013), Spatial spline regression models, Journal of the Royal Statistical Society, Series B, 75, 681-703.

See Also

link{FEMdensity}

Examples

#  ---------  Density on right triangle  --------------

#  Define the locations of the vertices of the right triangle
pts <- matrix(c(0,0, 1,0, 0,1), 3, 2, byrow=TRUE)
npts <- dim(pts)[1]
#  Specify the single triangle defined by these vertices.
#  The vertices are listed in counter-clockwise order
tri  <- matrix(c(1,2,3),1,3)
ntri <- dim(tri)[1]
#  Set up the FEM basis object for this region
RtTriBasis <- create.FEM.basis(pts, NULL, tri, 1)
plotFEM.mesh(pts, tri, RtTriBasis)
#  List object containing details of nodes.
nodeList <- makenodes(pts,tri,1)
K1 <- stiff.FEM(RtTriBasis)
#  Define the true log density, which is flat with height 0
ZeroFn <- function(x,y) {
  xdim <- dim(x)
  ZeroIntens <- matrix(0,xdim[1],xdim[1])
  return(ZeroIntens)
}
#  Compute of probabilities for each triangle of having a
#  location withinx it.
intDensityVec <- triDensity(pts, tri, ZeroFn)
#  number of random points required
N <- 100
#  generate random points ... define the function
obspts <- randomFEMpts(N, pts, tri, intDensityVec)
#  plot the random points
points(obspts[,1],obspts[,2])
#  Define a starting value for the coefficient vector of length 3
cvec <- matrix(0,npts,1)
#  Estimate the smooth density surface with no smoothing
densityList <- smooth.FEM.density(obspts, cvec, RtTriBasis, dbglev=2, iterlim=10)
#  The estimate of the coefficient vector
cvec <- densityList$cvec
#  Define the log density FEM functional data object
lnlamfd  <- fd(cvec,  RtTriBasis)
#  Plot the log density surface 
Xgrid <- seq(0,1,len=51)
Ygrid <- Xgrid
plotFEM.fd(lnlamfd, Xgrid, Ygrid)
#  Plot the log density surface
plotFEM.fd(lnlamfd, Xgrid, Ygrid)
#  Plot the log density surface using function contour
logdensitymat <- matrix(0,51,51)
for (i in 1:51) {
  for (j in 1:51) {
    logdensitymat[i,j] <- eval.FEM.fd(matrix(c(Xgrid[i],Ygrid[j]),1,2),lnlamfd)
  }
}
contour(Xgrid, Ygrid, logdensitymat)
#  Plot the density surface using function contour
densitymat <- matrix(0,51,51)
for (i in 1:51) {
  for (j in 1:51) {
    densitymat[i,j] <- exp(eval.FEM.fd(matrix(c(Xgrid[i],Ygrid[j]),1,2),lnlamfd))
  }
}
contour(Xgrid, Ygrid, densitymat)

#  ---------- density on a unit square,  4 triangles, 5 vertices  ----------

#  Generate a unit square with a node in its center defining four
#  triangles and five nodes.
result <- squareMesh(1)
pts    <- result$p
edg    <- result$e
tri    <- result$t
npts   <- dim(pts)[1]
ntri   <- dim(tri)[1]
#  Compute a sine*cosine intensity surface.
SinCosIntensFn <- function(x,y) {
  return(sin(2*pi*x)*cos(2*pi*y))
}
logDensityVec <- triDensity(pts, tri, SinCosIntensFn)
#  Set up and plot an FEM basis object
par(cex.lab=2)
SquareBasis1 <- create.FEM.basis(pts, edg, tri)
plotFEM.mesh(pts, tri)
#  generate random points
N = 100
obspts <- randomFEMpts(N, pts, tri, logDensityVec)
#  plot the random points
points(obspts[,1],obspts[,2])
#  Estimate the smooth density surface with light smoothing
order <- 1
nodeList <- makenodes(pts,tri,order)
K1 <- stiff.FEM(SquareBasis1)
lambda <- 1e-4
#  define a random coefficient vector
cvec  <- matrix(0,npts,1)
#  Estimate the smooth density surface with no smoothing
densityList <- smooth.FEM.density(obspts, cvec, SquareBasis1, dbglev=2, iterlim=10)
#  The estimate of the coefficient vector
cvec <- densityList$cvec
#  Define the log density FEM functional data object
lnlamfd  <- fd(cvec,  SquareBasis1)
#  Plot the log density surface 
Xgrid <- seq(0,1,len=51)
Ygrid <- Xgrid
plotFEM.fd(lnlamfd, Xgrid, Ygrid)
#  Plot the log density surface
plotFEM.fd(lnlamfd, Xgrid, Ygrid)
#  Plot the log density surface using function contour
logdensitymat <- matrix(0,51,51)
for (i in 1:51) {
  for (j in 1:51) {
    logdensitymat[i,j] <- eval.FEM.fd(matrix(c(Xgrid[i],Ygrid[j]),1,2),lnlamfd)
  }
}
contour(Xgrid, Ygrid, logdensitymat)
#  Plot the density surface using function contour
densitymat <- matrix(0,51,51)
for (i in 1:51) {
  for (j in 1:51) {
    densitymat[i,j] <- exp(eval.FEM.fd(matrix(c(Xgrid[i],Ygrid[j]),1,2),lnlamfd))
  }
}
contour(Xgrid, Ygrid, densitymat)

SpatialfdaR documentation built on Oct. 11, 2022, 5:06 p.m.