UDXappend2Ddata

   UDXappend2Ddata(filename,p,t,u,attr_name,attr_rank,attr_shape)

   Apends data to a file in DX form.
   Only one variable can be written to the file
   variable must be a scalar, vector or tensor of doubles   
   mesh data in the file must be consistent with this variable

   x
   attr_name  = name of the variable                   (type string)
   attr_rank  = rank of variable data                  (0 for scalar, 1 for vector, etc.)
   attr_shape = number of components of variable data  (assumed 1 for scalar)