#$
#$=head1 NAME
#$
#$helix - module containing allocate and deallocate of a  helix filter
#$
#$=head1 SYNOPSIS
#$
#$C<call allocatehelix(aa,nh)>
#$
#$C<call deallocatehelix(aa)>
#$
#$=head1 INPUT PARAMETERS
#$
#$=over 4
#$
#$=item aa - type(helix) 
#$
#$      Filter
#$
#$=item nh - integer
#$
#$      Number of coefs in filter
#$
#$=back
#$
#$=head1 DESCRIPTION
#$
#$Allocate and deallocation of helix filter.
#$
#$=head1 COMMENTS
#$
#$type(filter) :
#$
#$=over 4
#$
#$=item flt - C<real(:)> (nh) 
#$
#$      filter coefficients
#$
#$=item lag - C<real(:)> (nh) 
#$
#$      filter lags
#$
#$=item mis - C<real(:)>  (nd) 
#$
#$      boundary conditions
#$
#$=back
#$
#$=head1 SEE ALSO
#$
#$L<nhelix>,L<mshelix>
#$
#$=head1 LIBRARY
#$
#$B<geef90>
#$
#$=cut 
module helix {                                  # DEFINE helix filter type
  type filter {             
    real,    dimension( :), pointer :: flt      # (nh) filter coefficients
    integer, dimension( :), pointer :: lag      # (nh) filter lags
    logical, dimension( :), pointer :: mis      # (nd) boundary conditions
  }
contains
  subroutine allocatehelix( aa, nh ) {		# allocate a filter
    type( filter) :: aa
    integer       :: nh				# count of filter coefs (excl 1)
    allocate( aa%flt( nh), aa%lag( nh))		# allocate filter and lags.
    nullify( aa%mis)				# set null pointer for "mis".
    aa%flt = 0.					# zero filter coef values
  }
  subroutine deallocatehelix( aa) {		# destroy a filter
    type( filter) :: aa
    deallocate( aa%flt, aa%lag)			# free memory
    if( associated( aa%mis))			# if logicals were allocated
        deallocate( aa%mis)			#                     free them
  }
}