From 7dfcc480ba1e19bd3232349fc733caef94034292 Mon Sep 17 00:00:00 2001
From: stainer_t <thomas.stainer@oecd-nea.org>
Date: Mon, 8 Sep 2025 13:48:49 +0200
Subject: Initial commit from Polytechnique Montreal

---
 Dragon/src/MCGDYA.f | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 Dragon/src/MCGDYA.f

(limited to 'Dragon/src/MCGDYA.f')

diff --git a/Dragon/src/MCGDYA.f b/Dragon/src/MCGDYA.f
new file mode 100644
index 0000000..8d39758
--- /dev/null
+++ b/Dragon/src/MCGDYA.f
@@ -0,0 +1,74 @@
+*DECK MCGDYA
+      SUBROUTINE MCGDYA(NMU,ZMU,WZMU,NANGL,CAZ1,CAZ2,IL,IM,ILP,IMP,MM)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Returns the dyadic matrix of Eq. (43).
+*
+*Copyright:
+* Copyright (C) 2015 Ecole Polytechnique de Montreal
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version.
+*
+*Author(s): A. Hebert
+*
+*Parameters: input
+* NMU     number of polar angles.
+* ZMU     polar quadrature set in 2D.
+* WZMU    polar quadrature set in 2D.
+* NANGL   number of azimuthal angles.
+* CAZ1    first azimuthal cosines.
+* CAZ2    second azimuthal cosines.
+* IL      spherical harmonics index.
+* IM      spherical harmonics index.
+* ILP     spherical harmonics index.
+* IMP     spherical harmonics index.
+*
+*Parameters: output
+* MM      dyadic matrix.
+*
+*-----------------------------------------------------------------------
+*
+      IMPLICIT DOUBLE PRECISION(A-H,O-Z)
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER NMU, IL, IM, ILP, IMP
+      REAL ZMU(NMU),WZMU(NMU)
+      DOUBLE PRECISION CAZ1(NANGL),CAZ2(NANGL),MM(2,2)
+*
+      REAL PNSH
+      DOUBLE PRECISION DYAD(2,2)
+      REAL, DIMENSION(:), ALLOCATABLE :: WW, MU, ETA, XI
+      DOUBLE PRECISION, PARAMETER :: PI=3.14159265358979323846264338328
+*
+      ALLOCATE(WW(2*NMU*NANGL), MU(2*NMU*NANGL), ETA(2*NMU*NANGL),
+     >         XI(2*NMU*NANGL))
+      DO IANGLE=1,NANGL
+        DO IMU=1,NMU
+          MU((IANGLE-1)*NMU+IMU)=SQRT(1.0-1.0/ZMU(IMU)**2)
+          ETA((IANGLE-1)*NMU+IMU)=REAL(CAZ1(IANGLE)/ZMU(IMU))
+          XI((IANGLE-1)*NMU+IMU)=REAL(CAZ2(IANGLE)/ZMU(IMU))
+          WW((IANGLE-1)*NMU+IMU)=WZMU(IMU)*MU((IANGLE-1)*NMU+IMU)
+          MU((NANGL+IANGLE-1)*NMU+IMU)=-MU((IANGLE-1)*NMU+IMU)
+          ETA((NANGL+IANGLE-1)*NMU+IMU)=-ETA((IANGLE-1)*NMU+IMU)
+          XI((NANGL+IANGLE-1)*NMU+IMU)=-XI((IANGLE-1)*NMU+IMU)
+          WW((NANGL+IANGLE-1)*NMU+IMU)=WW((IANGLE-1)*NMU+IMU)
+        ENDDO
+      ENDDO
+      MM(:,:)=0.0D0 ; WSUM=0.0D0 ;
+      DO IANGLE=1,2*NMU*NANGL
+        DYAD=MATMUL(RESHAPE((/ ETA(IANGLE), XI(IANGLE) /),(/ 2, 1 /)),
+     >              RESHAPE((/ ETA(IANGLE), XI(IANGLE) /),(/ 1, 2 /)))
+        RLM=PNSH(IL,IM,MU(IANGLE),ETA(IANGLE),XI(IANGLE))
+        RLMP=PNSH(ILP,IMP,MU(IANGLE),ETA(IANGLE),XI(IANGLE))
+        WSUM=WSUM+WW(IANGLE)
+        MM=MM+WW(IANGLE)*RLM*RLMP*DYAD
+      ENDDO
+      MM=(2.0D0*ILP+1.0D0)/WSUM*MM
+      DEALLOCATE(WW, MU, ETA, XI)
+      RETURN
+      END
-- 
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