Clarify type 2 (advances) polyphase and Transposed Direct form.

applications/lofar2/model/pfb_os/dsp_study_erko.txt

@@ -1269,9 +1269,15 @@ c) s-plane and z-plane
        where:
            rp[n] = h(Qn - p),  -p for clockwise with advances z^(+1)
 
-           Rq(z) = E_{Q-1-p}(z),   so flipud phases, but keep coefficient order
+           Rp(z) = E_{Q-1-p}(z),   so flipud Eq phases, but keep coefficient order
                                    per phase
 
+    ??? Is Type II polyphase same as Transposed Direct Form ???, because both still
+    implement H(z), they only yield different implementation structures. For Type 1
+    and Direct-Form the delay line goes from top to bottom in drawings. For Type 2
+    and Transposed we also want to draw the delay line from top to bottom (Fig 4.3.4,
+    Fig 4.3.11, Fig 4.5.6), but then we need to flipud the Eq phases.
+
   . Phase q of h(n) with Q - 1 zeros, so [VAIDYANATHAN Fig 4.3.1]:
 
      h[n] --> z^(-q) --> Q:1 --> eq[n]