diff --git a/qpms/scatsystem.c b/qpms/scatsystem.c
index abe395a..7185744 100644
--- a/qpms/scatsystem.c
+++ b/qpms/scatsystem.c
@@ -373,9 +373,25 @@ qpms_scatsys_t *qpms_scatsys_apply_symmetry(const qpms_scatsys_t *orig, const qp
   ss->p = realloc(ss->p, sizeof(qpms_particle_tid_t) * ss->p_count); ss->p_capacity = ss->p_count;
 
   ss->sym = sym;
+
+  // Set ss->fecv_size and ss->fecv_pstarts
+  ss->fecv_size = 0;
+  ss->fecv_pstarts = malloc(ss->p_count * sizeof(size_t));
+  for (qpms_ss_pi_t pi = 0; pi < ss->p_count; ++pi) {
+    ss->fecv_pstarts[pi] = ss->fecv_size;
+    ss->fecv_size += ss->tm[ss->p[pi].tmatrix_id]->spec->n; // That's a lot of dereferencing!
+  }
+
   return ss;
 }
 
-  
 
+void qpms_scatsys_free(qpms_scatsys_t *ss) {
+  free(ss->tm);
+  free(ss->p);
+  free(ss->fecv_pstarts);
+  free(ss->tm_sym_map);
+  free(ss->p_sym_map);
+  free(ss);
+}
 
diff --git a/qpms/scatsystem.h b/qpms/scatsystem.h
index b0f7466..f200bb2 100644
--- a/qpms/scatsystem.h
+++ b/qpms/scatsystem.h
@@ -212,6 +212,12 @@ typedef struct qpms_scatsys_t {
 	qpms_ss_pi_t *p_sym_map; ///< Which particles map onto which by the symmetry ops.
 	///< p_sym_map[idi + pi * sym->order] gives the index of pi-th particle under the idi'th sym op.
 	qpms_ss_tmi_t *tm_sym_map; ///< Which t-matrices map onto which by the symmetry ops. Lookup by tm_sum_map[idi + tmi * sym->order].
+	size_t fecv_size; ///< Number of elements of a full excitation coefficient vector size. 
+	//size_t *saecv_sizes; ///< NI. Number of elements of symmetry-adjusted coefficient vector sizes (order as in sym->irreps). 
+
+	size_t *fecv_pstarts; ///< Indices of where pi'th particle's excitation coeffs start in a full excitation coefficient vector.
+	//size_t **saecv_pstarts; ///< NI. Indices of where pi'th particle's excitation coeff start in a symmetry-adjusted e.c.v.
+	///**< First index is irrep index as in sym->irreps, second index is particle index. */
 
 	// TODO shifted origin of the symmetry group etc.
 	// TODO some indices for fast operations here.