diff --git a/.gitignore b/.gitignore
index f4ad6b9..9526a5b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,4 +3,6 @@
 *.swp
 *.out
 *.pdf
+*.o
 docs/*
+qpms/qpms_c.c
diff --git a/qpms/scatsystem.h b/qpms/scatsystem.h
index 188e071..f1f2438 100644
--- a/qpms/scatsystem.h
+++ b/qpms/scatsystem.h
@@ -412,6 +412,30 @@ qpms_scatsys_t *qpms_scatsys_apply_symmetry(const qpms_scatsys_t *orig, const st
 /// Destroys the result of qpms_scatsys_apply_symmetry or qpms_scatsys_load.
 void qpms_scatsys_free(qpms_scatsys_t *s);
 
+/// Projects a "big" matrix onto an irrep.
+/** TODO doc */
+qpms_errno_t qpms_scatsys_irrep_pack_matrix(complex double *target_packed,
+		const complex double *orig_full, const qpms_scatsys_t *ss,
+		qpms_iri_t iri);
+
+/// Transforms a big "packed" matrix into the full basis.
+/** TODO doc */
+qpms_errno_t qpms_scatsys_irrep_unpack_matrix(complex double *target_full,
+		const complex double *orig_packed, const qpms_scatsys_t *ss,
+		bool add);
+
+/// Projects a "big" vector onto an irrep.
+/** TODO doc */
+qpms_errno_t qpms_scatsys_irrep_pack_vector(complex double *target_packed,
+		const complex double *orig_full, const qpms_scatsys_t *ss,
+		qpms_iri_t iri);
+
+/// Transforms a big "packed" vector into the full basis.
+/** TODO doc */
+qpms_errno_t qpms_scatsys_irrep_unpack_vector(complex double *target_full,
+		const complex double *orig_packed, const qpms_scatsys_t *ss,
+		bool add);
+
 /// NOT IMPLEMENTED Dumps a qpms_scatsys_t structure to a file.
 qpms_errno_t qpms_scatsys_dump(qpms_scatsys_t *ss, char *path);
 
diff --git a/tests/interptest.py b/tests/interptest.py
new file mode 100644
index 0000000..0458f07
--- /dev/null
+++ b/tests/interptest.py
@@ -0,0 +1,7 @@
+
+from qpms import Particle, CTMatrix, BaseSpec, FinitePointGroup, ScatteringSystem, TMatrixInterpolator
+bspec1 = BaseSpec(lMax = 1)
+
+tmfile = '/home/mmn/tmp/cylinder_50nm_lMax4_cleaned.TMatrix'
+interp = TMatrixInterpolator(tmfile, bspec1)
+interp(3)
diff --git a/tests/scatsys.py b/tests/scatsys.py
new file mode 100644
index 0000000..3367200
--- /dev/null
+++ b/tests/scatsys.py
@@ -0,0 +1,13 @@
+from qpms import Particle, CTMatrix, BaseSpec, FinitePointGroup, ScatteringSystem
+from qpms.symmetries import point_group_info
+import numpy as np
+
+sym = FinitePointGroup(point_group_info['D3h'])
+bspec2 = BaseSpec(lMax=2)
+bspec1 = BaseSpec(lMax=1)
+t1 = CTMatrix(bspec1, np.diag(np.random.random(len(bspec1))))
+t2 = CTMatrix(bspec2, np.diag(np.random.random(len(bspec2))))
+p1 = Particle((1,2,),t1)
+p2 = Particle((1,2,3),t1)
+p3 = Particle((0.1,2),t2)
+ss = ScatteringSystem([p1, p2, p3], sym)