tweak a_lm rotation

interpol_ng/alm.h

@@ -212,20 +212,21 @@ class wigner_d_risbo_openmp
 template<typename T> void rotate_alm (Alm<complex<T>> &alm,
   double psi, double theta, double phi)
   {
-  MR_assert (alm.Lmax()==alm.Mmax(),
-    "rotate_alm: lmax must be equal to mmax");
   auto lmax=alm.Lmax();
+  MR_assert (lmax==alm.Mmax(),
+    "rotate_alm: lmax must be equal to mmax");
+
+  if (theta!=0)
+    {
     vector<complex<double> > exppsi(lmax+1), expphi(lmax+1);
     for (size_t m=0; m<=lmax; ++m)
       {
       exppsi[m] = polar(1.,-psi*m);
       expphi[m] = polar(1.,-phi*m);
       }
-
-  wigner_d_risbo_openmp rec(lmax,theta);
-
     vector<complex<double> > almtmp(lmax+1);
 size_t nthreads=1;
+    wigner_d_risbo_openmp rec(lmax,theta);
     for (size_t l=0; l<=lmax; ++l)
       {
       const auto &d(rec.recurse());
@@ -260,6 +261,16 @@ size_t nthreads=1;
         alm(l,m) = complex<T>(almtmp[m]*expphi[m]);
       }
     }
+  else
+    {
+    for (size_t m=0; m<=lmax; ++m)
+      {
+      auto ang = polar(1.,-(psi+phi)*m);
+      for (size_t l=m; l<=lmax; ++l)
+        alm(l,m) *= ang;
+      }
+    }
+  }
 #endif
 }
 

interpol_ng/demo.py

@@ -86,8 +86,9 @@ bar2 = np.zeros((nth,nph))
 blmTfull = np.zeros(slmT.size)+0j
 blmTfull[0:blmT.size] = blmT
 for ith in range(nth):
+    rbeamth=interpol_ng.rotate_alm(blmTfull, lmax, ptg[ith,0,2],ptg[ith,0,0],0)
     for iph in range(nph):
-        rbeam=interpol_ng.rotate_alm(blmTfull, lmax, ptg[ith,iph,2],ptg[ith,iph,0],ptg[ith,iph,1])
+        rbeam=interpol_ng.rotate_alm(rbeamth, lmax, 0, 0, ptg[ith,iph,1])
         bar2[ith,iph] = convolve(slmT, rbeam, lmax).real
 plt.subplot(2,2,2)
 plt.imshow(bar2)