Dummy (zero) T-matrix generator

qpms/cytmatrices.pyx

@@ -286,6 +286,10 @@ cdef class TMatrixGenerator:
             self.holder = what
             self.g.function = qpms_tmatrix_generator_interpolator
             self.g.params = <void*>(<TMatrixInterpolator?>self.holder).rawpointer()
+        elif what == 0:
+            self.holder = 0
+            self.g.function = qpms_tmatrix_generator_zero
+            self.g.params = <void*> 0
         elif callable(what):
             warnings.warn("Custom python T-matrix generators are an experimental feature. Also expect it to be slow.")
             self.holder = what
@@ -403,3 +407,15 @@ cdef class TMatrixGenerator:
             EpsMuGenerator(outside), EpsMuGenerator(inside),
             ArcFunction(__ArcCylinder(r, h)), *args, **kwargs))
 
+    @staticmethod
+    def dummy():
+        """Returns a dummy T-matrix generator (returns a zero T-matrix).
+
+        Returns
+        -------
+        tmgen_dummy : TMatrixGenerator
+        """
+        return tmgen_dummy
+
+# pre-generate a dummy TMatrixGenerator (which returns zero T-matrix)
+tmgen_dummy = TMatrixGenerator(0)

qpms/qpms_cdefs.pxd

@@ -496,6 +496,7 @@ cdef extern from "tmatrices.h":
     qpms_errno_t qpms_tmatrix_generator_interpolator(qpms_tmatrix_t *t, cdouble omega, const void *params)
     qpms_errno_t qpms_tmatrix_generator_sphere(qpms_tmatrix_t *t, cdouble omega, const void *params)
     qpms_errno_t qpms_tmatrix_generator_constant(qpms_tmatrix_t *t, cdouble omega, const void *params)
+    qpms_errno_t qpms_tmatrix_generator_zero(qpms_tmatrix_t *t, cdouble omega, const void *params)
     struct qpms_tmatrix_generator_sphere_param_t:
         qpms_epsmu_generator_t outside
         qpms_epsmu_generator_t inside

qpms/tmatrices.c

@@ -988,6 +988,12 @@ qpms_errno_t qpms_tmatrix_generator_constant(qpms_tmatrix_t *t,
   return QPMS_SUCCESS;
 }
 
+qpms_errno_t qpms_tmatrix_generator_zero(qpms_tmatrix_t *t,
+    complex double omega_ignored, const void *params_ignored) {
+  memset(t->m, 0, SQ(t->spec->n)*sizeof(*(t->m)));
+  return QPMS_SUCCESS;
+}
+
 void qpms_tmatrix_operation_clear(qpms_tmatrix_operation_t *f) {
   switch(f->typ) {
     case QPMS_TMATRIX_OPERATION_NOOP:

qpms/tmatrices.h

@@ -258,6 +258,7 @@ _Complex double *qpms_apply_tmatrix(
  * qpms_tmatrix_generator_interpolator()
  * qpms_tmatrix_generator_sphere()
  * qpms_tmatrix_generator_constant()
+ * qpms_tmatrix_generator_zero()
  */
 typedef struct qpms_tmatrix_generator_t {
 	qpms_errno_t (*function) (qpms_tmatrix_t *t, ///< T-matrix to fill.
@@ -279,11 +280,20 @@ qpms_tmatrix_t *qpms_tmatrix_init_from_generator(
  * the same base spec.
  */
 qpms_errno_t qpms_tmatrix_generator_constant(qpms_tmatrix_t *t,
-		_Complex double omega,
+		_Complex double omega_ignored,
 		/// Source T-matrix, real type is (const qpms_tmatrix_t*).
 		const void *tmatrix_orig
 		);
 
+/// Dummy implementation of qpms_tmatrix_generator_t, yielding a zero matrix.
+/**
+ * This effectively represents a part of the background medium without
+ * any scatterer present.
+ */
+qpms_errno_t qpms_tmatrix_generator_zero(qpms_tmatrix_t *t,
+    _Complex double omega_ignored,
+    const void *params_ignored);
+
 /* Fuck this, include the whole <gsl/gsl_spline.h>
 typedef struct gsl_spline gsl_spline; // Forward declaration for the interpolator struct
 typedef struct gsl_interp_type gsl_interp_type;