path: root/src/maple/gfa.maple

# gfa.maple -- low-level gridfn array "database"
# $Header$
#
# ***** gridfn arrays *****
# ***** functional dependences *****
# make_gfa - construct a new gridfn array
# assert_fnd_exists - assert (verify) that a given gridfn array fnd form exists
# Maple_name - Maple name of functional-dependence form
#
# index/symmetric3_23 - Maple indexing fn for rank 3 array sym on axes 23
#
# print_symmetric3_23 - prettyprint a symmetric3_23 array
#

################################################################################

#
# ***** gridfn arrays *****
#

#
# The basic data objects for the Maple code are grid function arrays,
# a.k.a. gridfn arrays, such as the metric g_dd, the Christoffel symbols
# Gamma_udd, etc etc.
#
# By convention, the name of a nonscalar geometric object ends with an 
# underscore ("_") followed by a sequence of "d" or "u" specifying whether
# the indices are down (covariant) or up (contravariant).  Thus, for
# example, g_dd is the covariant metric, while g_uu is the inverse metric.
#
# Scalar geometric objects are represented by Maple scalars, while
# nonscalar objects (often but not necessarily tensors) are represented
# by Maple arrays, using Maple indexing functions for any symmetries
# or sparsity.  For example, the metric  g_dd  is represented by an
# array
#	array(1..N, 1..N, symmetric)
# By convention, for a symmetric array of this type, we only compute
# the upper triangle.
#

################################################################################

#
# ***** functional dependences *****
#

#
# Within the Maple code, we distinguish between two distinct forms
# that a gridfn array may take:
# - The "inert" form of a gridfn array represents (only) the symmetries,
#   zero (or nonzero but constant) elements, and indexing semantics of
#   the gridfn array.
# - The "functional dependence" form of a gridfn array additionally
#   represents how that gridfn array is computed from other gridfn
#   arrays.
#
# For example, consider the inverse metric  g_uu .  It's inert form
# is a 3*3 symmetric array, with all elements being unassigned symbols
# (i.e. evaluating to themselves, as is usual in Maple).  It's functional
# dependence form, in contrast, is also a 3*3 symmetric array, but its
# elements are expressions giving the inverse-metric elements in terms
# of components of the metric and/or the metric determinant.
#
# Any given gridfn array may exist in either or (the usual case) both
# an inert form and a functional dependence forms.  There may also be
# multiple functional dependence forms, corresponding to alternative
# formulas for its computation.)
#
# The inert form of a gridfn array is represented by a Maple variable
# or array (see below) of the same name (eg  g_uu ), unassigned except
# for any symmetries and/or zero components the gridfn array has.
#
# The functional dependence form of a gridfn array is represented by
# a Maple array (see below) with a name formed by appending "__fnd"
# to the gridfn array's name (eg  g_uu__fnd ); this array has the same
# symmetries as the corresponding inert Maple array, but only those
# elements needed will be assigned.  If there are multiple functional
# dependence forms, by convention each uses a name beginning in "__"
# and ending in "fnd", eg  H__ps_fnd .
#
# The PDE compiler normally generates C code referring to the (inert)
# gridfn array names, so these should be valid C variable names.
#

#
# To allow some run-time error checking, we keep a global table
# of all the gridfn array functional-dependence forms:
#	`gfa/fnd_table`
#	... table index is  gfa__fnd_name
#	... table value is  true
# assert_fnd_exists() uses this table to verify that a given gridfn
# array functional-dependence form does indeed exist.
#

#
# Functional-dependence forms may be multilevel, as in (eg)
#  g_dd__Kerr_fnd__ps_fnd .  cat() may be used to combine names in
# this manner.
#

################################################################################

#
# This function makes the Maple representation of a single gridfn array.
#
# Arguments:
# gfa_name = (out*) The Maple variable to be created for the gridfn
#		    array.  This argument should be passed as an
#		    unevaluated (quoted) name.
# fnd_name_set = (in) A set of functional dependence types the gridfn
#		      array is to have.  The set's members should be
#		      drawn from from {inert, fnd, ...} as appropriate,
#		      where the special value  inert  refers to the
#		      inert form.
# index_bounds = (in) The list of index bounds for the gridfn array,
# index_fn = (in) The name of the array indexing function, if any, or
#		  'none' if the gridfn array has no symmetries and thus
#		  should be represented by a Maple array with the standard
#		  "ordinary array" indexing semantics.
#
# Thus, for example, the calls
#	make_gfa('g', {inert, fnd}, [], none);
#	make_gfa('g_dd', {inert}, [1..N, 1..N], symmetric);
#	make_gfa('R_dd', {inert, fnd}, [1..N, 1..N], symmetric);
#	make_gfa('Gamma_udd', {inert, fnd}, [1..N, 1..N, 1..N], symmetric3_23);
# would set up the Maple representations of the metric determinant,
# the metric, the Ricci tensor, and the Christoffel symbols respectively.
#
make_gfa :=
proc(gfa_name::name,
     fnd_name_set::set(name),
     index_bounds::list(integer..integer),
     index_fn::{identical(none), name})	# note "name" here, not "procedure",
					# since we'll get the name of the
					# indexing fn, which may not have
					# been assigned its procedure yet
global N, `gfa/fnd_table`;
local fnd_name, var_name, index_fn_seq;

# firewall checks
if (not type(N, integer))
   then ERROR("must set up coordinates first!");
end if;
if ((index_bounds = []) and (index_fn <> 'none'))
   then ERROR("not meaningful to specify a symmetry function for a scalar!",
	      "   gfa_name=",gfa_name);
end if;

# create the Maple variable(s)
	for fnd_name in fnd_name_set
	do
	var_name := Maple_name(gfa_name, fnd_name);
	if (assigned(`gfa/fnd_table`[eval(var_name,1)]))
	   then ERROR("duplicate gfa/fnd definition!",
		      "   gfa_name=", gfa_name,
		      "   fnd_name_set=", fnd_name_set);
	end if;
	`gfa/fnd_table`[eval(var_name,1)] := true;
	if (index_bounds = [])
	   then # scalar
		unassign(  eval(var_name,1)  );
	   else # array
		if (index_fn = 'none')
		   then index_fn_seq := NULL;
		   else index_fn_seq := index_fn;
		end if;
		assign(
		    eval(var_name,1) = array(index_fn_seq, op(index_bounds))
		      );
	end if;
	end do;

NULL;
end proc;

################################################################################

#
# This function checks that a given gridfn array functional-dependence
# form exists.  If so, this function is a no-op; if not, this function
# calls ERROR().  Hence after calling this function, the caller can assume
# that the given functional-dependence form does indeed exist.
#
# This function may be called with either 1 or 2 arguments (the two
# types of calls are equivalent).
#
# Arguments (1-argument form):
# gfa_name = The name of the gridfn array itself.  In this case the
#	     fnd name defaults to `fnd`.
#
# Arguments (2-argument form):
# gfa_name = The name of the gridfn array itself, eg `g_dd`.
# fnd_name = The name of the fnd itself, eg `fnd`.
#
assert_fnd_exists :=
proc(gfa_name::name, fnd_name::name)
global `gfa/fnd_table`;
local var_name;

var_name := Maple_name(gfa_name, args[2..nargs]);

if (not assigned(`gfa/fnd_table`[eval(var_name,1)]))
   then ERROR("functional-dependence form doesn't exist!",
	      "var_name=",var_name);
end if;
end proc;

################################################################################

#
# This function computes the Maple name corresponding to a given
# gridfn array and functional dependence form.
#
# Arguments:
# gfa_name = The name of the gridfn array itself, eg `g_dd`.
# fnd_name = (optional)
#	     The name of the functional-dependence form, eg `fnd`,
#	     or the special name 'inert'.  If this argument is omitted
#	     it defaults to 'inert'.
#
Maple_name :=
proc(gfa_name::name, fnd_name::name)
if ((nargs = 1) or (fnd_name = 'inert'))
   then return gfa_name;
   else return cat(gfa_name, "__", fnd_name);
end if;
end proc;

################################################################################
################################################################################
################################################################################

#
# This function is a Maple indexing function for a rank 3 table/array
# which is symmetric in the 2nd and 3rd indices.  This function is
# called automagically by Maple whenever a component of such an array
# is referenced.
#
# The ordering is done using the Maple  sort()  function, which sorts
# numbers numerically, strings lexicographically, and "other things"
# by machine address.
#
# Arguments:
# ilist = (in) The indices to be used.  There must be exactly 3 of these.
# tab = (in out) The table/array to be indexed.  This uses any remaining
#		 indexing methods.
# vlist = (optional)
#	  If present, this is a list of the values to be assigned to
#	  the (lvalue) table entry.
#
`index/symmetric3_23` :=
proc(ilist::list, tab::table, vlist::list)
local k, i, j, index_seq;

if (not (nops(ilist) = 3))
   then ERROR(`must have exactly 3 indices!`);
end if;

# ... note we need eval() here to get actual integers,
#     rather than variable names whose values are integers
k := eval(ilist[1]);
i := eval(ilist[2]);
j := eval(ilist[3]);

index_seq := k, op(sort([i,j]));

if (nargs = 2)
   then return tab[index_seq];		# rvalue
   else tab[index_seq] := op(vlist);	# lvalue
end if;
end proc;

################################################################################
################################################################################
################################################################################

#
# This function prettyprints a symmetric3_23 array
#
# Arguments:
# A = (in) The array to be prettyprinted
#
# Results:
# There is no explicit result; the array is prettyprinted as a side effect.
#
print_symmetric3_23 :=
proc(A::array)
local bounds, k, i, j, M23;

if (op(1, eval(A)) <> 'symmetric3_23')
   then ERROR(`can only print symmetric3_23 arrays`);
end if;

bounds := op(2, eval(A));

M23 := array(bounds[2..3], symmetric);

	for k in $(bounds[1]) do

		for i in $(bounds[2]) do
		for j in $(bounds[3]) do
		if (i <= j)		# only need upper triangle in (i,j)
		   then M23[i,j] := A[k,i,j];
		end if;
		end do;
		end do;

	printf("[%d] = \n", k);
	print(M23);
	end do;

NULL;
end proc;