1 files changed, 123 insertions, 0 deletions
diff --git a/Utilib/src/ALINDX.f b/Utilib/src/ALINDX.f
new file mode 100644
index 0000000..9a5005c
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+++ b/Utilib/src/ALINDX.f
@@ -0,0 +1,123 @@
+*DECK ALINDX
+      SUBROUTINE ALINDX(n,arr,indx)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* indexes an array arr(1:n) such that abs(arr(indx(j))) is in descending
+* order for j=1:n.
+* 
+*Copyright:
+* Copyright (C) 2020 Ecole Polytechnique de MontCOMPLEX(KIND=8)
+* 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
+* n       size of the array a.
+* a       array a.
+*
+*Parameters: output
+* indx    indexing vector.
+*
+*-----------------------------------------------------------------------
+*
+*----
+*  subroutine arguments
+*----
+      INTEGER n,indx(n)
+      COMPLEX(KIND=8) arr(n)
+*----
+*  local variables
+*----
+      INTEGER nstack,i,indxt,ir,itemp,j,jstack,k,l
+      COMPLEX(KIND=8) a
+      INTEGER, parameter :: M=7
+      INTEGER, allocatable, dimension(:) :: istack
+*
+      nstack=2*ceiling(log(real(n))/log(2.0))
+      allocate(istack(nstack))
+      do j=1,n
+        indx(j)=j
+      enddo
+      jstack=0
+      l=1
+      ir=n
+    1 if(ir-l.lt.M) then
+        do j=l+1,ir
+          indxt=indx(j)
+          a=arr(indxt)
+          do i=j-1,l,-1
+            if(absc(arr(indx(i))).ge.absc(a)) goto 2
+            indx(i+1)=indx(i)
+          enddo
+          i=l-1
+    2     indx(i+1)=indxt
+        enddo
+        if(jstack.eq.0)go to 5
+        ir=istack(jstack)
+        l=istack(jstack-1)
+        jstack=jstack-2
+      else
+        k=(l+ir)/2
+        itemp=indx(k)
+        indx(k)=indx(l+1)
+        indx(l+1)=itemp
+        if(absc(arr(indx(l))).lt.absc(arr(indx(ir))))then
+          itemp=indx(l)
+          indx(l)=indx(ir)
+          indx(ir)=itemp
+        endif
+        if(absc(arr(indx(l+1))).lt.absc(arr(indx(ir)))) then
+          itemp=indx(l+1)
+          indx(l+1)=indx(ir)
+          indx(ir)=itemp
+        endif
+        if(absc(arr(indx(l))).lt.absc(arr(indx(l+1)))) then
+          itemp=indx(l)
+          indx(l)=indx(l+1)
+          indx(l+1)=itemp
+        endif
+        i=l+1
+        j=ir
+        indxt=indx(l+1)
+        a=arr(indxt)
+    3   i=i+1
+        if(absc(arr(indx(i))).gt.absc(a)) goto 3
+    4   j=j-1
+        if(absc(arr(indx(j))).lt.absc(a)) goto 4
+        if(j.ge.i) then
+          itemp=indx(i)
+          indx(i)=indx(j)
+          indx(j)=itemp
+          goto 3
+        endif
+        indx(l+1)=indx(j)
+        indx(j)=indxt
+        jstack=jstack+2
+        if(jstack.gt.nstack) call XABORT('ALINDX: nstack too small.')
+        if(ir-i+1.ge.j-l) then
+          istack(jstack)=ir
+          istack(jstack-1)=i
+          ir=j-1
+        else
+          istack(jstack)=j-1
+          istack(jstack-1)=l
+          l=i
+        endif
+      endif
+      goto 1
+    5 deallocate(istack)
+      return
+*
+      contains
+      function absc(val) result(aval)
+        ! definition of combined value for complex numbers
+        COMPLEX(kind=8), intent(in) :: val
+        REAL(kind=8) :: aval
+        aval=100.0d0*real(val)+aimag(val)
+      end function absc
+      END