R/vec2symmx.R

In mrparker909/MGLMRiem: Multivariate Generalized Linear Models on Riemannian Manifolds

# function mx = vec2symmx(v)
# %VEC2SYMMX converts vectors v to matrices mx.
# %
# %   mx = vec2symmx(v)
# %
# %   v is a set of n(n+1)/2 dimensional vectors to n by n matrices.
# %   mx is a set of n x n matrices.
# %
# %   See also INVEMBEDDINGR6, SYMMX2VEC
# 
# %   Hyunwoo J. Kim
# %   $Revision: 0.1 $  $Date: 2014/06/23 15:09:53 $
#   
#   [dimv ndata] = size(v);
#   n = (-1 + sqrt(1+8*dimv))/2;
#   mx = zeros(n,n,ndata);
#   k = 1;
#   for i=1:n
#   for j=i:n
#   mx(i,j,:) = v(k,:);
#   if i ~=j
#   mx(j,i,:) = v(k,:);
#   end
#   k = k + 1;
#   end
#   end
#   end

#' @export
vec2symmx <- function(v) {
#VEC2SYMMX converts vectors v to matrices mx.
#
#   mx = vec2symmx(v)
#
#   v is a set of n(n+1)/2 dimensional vectors to n by n matrices.
#   mx is a set of n x n matrices.
#
#   See also INVEMBEDDINGR6, SYMMX2VEC

#   Hyunwoo J. Kim
#   $Revision: 0.1 $  $Date: 2014/06/23 15:09:53 $
  
#   Migrated to R by Matthew RP Parker
#   $Revision: 0.2 $  $Date: 2019/06/17 $ 
  v <- t(v)
  if(is.null(dim(v))) {
    v <- t(t(v))
  }
  
  sR    <- sizeR(v)
  dimv  <- sR[1]
  ndata <- sR[2]
  
  n = (-1 + sqrt(1+8*dimv))/2
  mx = array(0, dim=c(n,n,ndata))
  k = 1
  for(i in 1:n) {
    for(j in i:n) {
      for(g in 1:ndata) {
        mx[i,j,g] = v[k,g]
        if(i !=j) {
          mx[j,i,g] = v[k,g]
        }
      }
      k = k + 1
    }
  }
  return(mx)
}