Writing down some plans on abstract t-matrices / particles.

Former-commit-id: 83722142c0b53f995c61f53a3c58320491b27843

qpms/groups.h

@@ -4,6 +4,22 @@
  * Right now, the instances of qpms_finite_group_t are created at compilation time
  * from source code generated by Python script TODO (output groups.c)
  * and they are not to be constructed dynamically.
+ *
+ * In the end, I might want to have a special type for 3D point groups
+ * or more specifically, for the closed subgroups of O(3), see
+ * https://en.wikipedia.org/wiki/Point_groups_in_three_dimensions.
+ * They consist of the seven infinite series of axial groups 
+ * (characterized by the series index, the axis direction, 
+ * and the index \a n of the \a n-fold rotational symmetry)
+ * and the seven remaining point groups + the finite groups.
+ * All off them have a quite limited number of generators
+ * (max. 4?; CHECKME).
+ * The goal is to have some representation that would enable to
+ *   1. fully describe the symmetries of abstract T-matrices/nanoparticles,
+ *   2. quickly determine e.g. whether one is a subgroup of another,
+ *   3. have all the irreps,
+ *   4. have all in C and without excessive external dependencies,
+ * etc.
  */
 #ifndef QPMS_GROUPS_H
 #define QPMS_GROUPS_H

qpms/scatsystem.h

@@ -301,4 +301,41 @@ qpms_errno_t qpms_scatsys_dump(qpms_scatsys_t *ss, char *path);
 /// NOT IMPLEMENTED Reads a qpms_scatsys_t structure from a file.
 qpms_scatsys_t *qpms_scatsys_load(char *path);
 
+
+
+#if 0
+// Abstract types that describe T-matrix/particle/scatsystem symmetries
+// To be implemented later. See also the thoughts in the beginning of groups.h.
+
+typedef *char qpms_tmatrix_id_t; ///< Maybe I want some usual integer type instead.
+
+///Abstract T-matrix type draft.
+/**
+ * TODO.
+ */
+typedef struct qpms_abstract_tmatrix_t{
+	qpms_tmatrix_id_t id;
+	/// Generators of the discrete point group under which T-matrix is invariant.
+	qpms_irot3_t *invar_gens;
+	/// Length of invar_gens.
+	qpms_gmi_t invar_gens_size;
+
+} qpms_abstract_tmatrix_t;
+
+
+typedef struct qpms_abstract_particle_t{
+} qpms_abstract_particle_t;
+
+/// An abstract particle, defined by its position and abstract T-matrix.
+typedef struct qpms_abstract_particle_t {
+	cart3_t pos; ///< Particle position in cartesian coordinates.
+	const qpms_abstract_tmatrix_t *tmatrix; ///< T-matrix; not owned by this.
+} qpms_abstract_particle_t;
+
+
+/** This is just an alias, as the same index can be used for 
+ * abstract T-matrices as well.
+ */
+typedef qpms_particle_tid_t qpms_abstract_particle_tid_t;
+#endif // 0
 #endif //QPMS_SCATSYSTEM_H