#$
#$=head1 NAME
#$
#$helderiv - helix derivative filter
#$
#$=head1 SYNOPSIS
#$
#$Initializer: C<call helderiv_init(n1,na)>
#$
#$Operator   : C<ierr=helderiv_lop(adj,add,pp,qq)>
#$
#$Close      : C<call helderiv_close()>
#$
#$=head1 PARAMETERS
#$
#$=over 4
#$
#$=item  n1 -  int     
#$
#$       number of samples in n1
#$
#$=item  na -  int     
#$
#$       number of coefs for filter
#$
#$=item adj -  logcal  
#$
#$      wheter or not run the adjoint
#$
#$=item add -  logical 
#$
#$       whether or not to add outout to data
#$
#$=item pp  -  C<real(:)>  
#$
#$      model
#$
#$=item qq  -  C<real(:)>  
#$
#$      data
#$
#$=back
#$
#$=head1 DESCRIPTION
#$
#$ Create and apply a helix derivative filter
#$
#$
#$=head1 SEE ALSO
#$
#$L<lapfac>, L<helicon>
#$
#$=head1 LIBRARY
#$
#$B<geef90>
#$
#$=cut
module helderiv {
use lapfac
use helicon
type( filter), private :: aa
#%  _init( n1, na)
integer, intent (in) :: n1, na
aa = lapfac2( 0.001, n1, na) 
call helicon_init( aa)
#% _lop (pp, qq)
integer stat1
stat1 = helicon_lop( adj, .false.,  pp, qq)
#% _close
call deallocatehelix( aa)
}