Array2ArrayDist <- function(Source, Data) {
   #=========================================
   # Find the distance^2 from the 
   #   Source vectors to Data vectors
   #=========================================
   n.Source <- dim(Source)[1]
   n.Data <- dim(Data)[1]
      # 2*the datum for use in cosine law
   Dx2 <- t(2*Data)                         
      # Length^2 of each datum vector
   Data.const <- apply(Data*Data, 1, sum)  
      # Length^2 of each source vector
   Source.const <- apply(Source*Source, 1, sum)  
      # Source^2 - 2*Source*Data + Data^2
      # Note that the first matrix has one col. for each datum.
   matrix(Source.const, n.Source, n.Data) -  Source%*%Dx2 +
                matrix(Data.const, n.Source, n.Data, byrow=T)
}