From 42a98ca518377949e8cfc902343a4b2d97a25564 Mon Sep 17 00:00:00 2001
From: schnetter <schnetter@b716e942-a2de-43ad-8f52-f3dfe468e4e7>
Date: Mon, 15 Jul 2002 17:15:29 +0000
Subject: Added thorn TGRtensor.  This is a utility thorn from the TGR code. 
 It contains generic tensor operations, some useful constants, code for
 numeric derivatives, interfaces to Lapack and BLAS, and interfaces for Cactus
 routines.

git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinUtils/TGRtensor/trunk@2 b716e942-a2de-43ad-8f52-f3dfe468e4e7
---
 src/derivs2.F90 | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 src/derivs2.F90

(limited to 'src/derivs2.F90')

diff --git a/src/derivs2.F90 b/src/derivs2.F90
new file mode 100644
index 0000000..4ca51bf
--- /dev/null
+++ b/src/derivs2.F90
@@ -0,0 +1,40 @@
+! $Header$
+
+#ifndef TGR_INCLUDED
+
+#include "cctk.h"
+#include "cctk_Parameters.h"
+
+module derivs2
+  implicit none
+  private
+  public get_2derivs
+  public get_2derivs2
+contains
+#endif
+  subroutine get_2derivs (a, f, pos, off, dx)
+    CCTK_REAL, intent(in)  :: a(*)
+    CCTK_REAL, intent(out) :: f(2)
+    integer,   intent(in)  :: pos, off(2)
+    CCTK_REAL, intent(in)  :: dx(2)
+    integer :: i
+    do i=1,2
+       f(i) = (a(pos+off(i)) - a(pos-off(i))) / (2*dx(i))
+    end do
+  end subroutine get_2derivs
+  subroutine get_2derivs2 (a, f, pos, off, dx)
+    CCTK_REAL, intent(in)  :: a(*)
+    CCTK_REAL, intent(out) :: f(2,2)
+    integer,   intent(in)  :: pos, off(2)
+    CCTK_REAL, intent(in)  :: dx(2)
+    integer :: i
+    do i=1,2
+       f(i,i) = (a(pos+off(i)) - 2*a(pos) + a(pos-off(i))) / dx(i)**2
+    end do
+    f(1,2) = (  a(pos-off(1)-off(2)) - a(pos+off(1)-off(2)) &
+         &    - a(pos-off(1)+off(2)) + a(pos+off(1)+off(2))) / (4*dx(1)*dx(2))
+    f(2,1) = f(1,2)
+  end subroutine get_2derivs2
+#ifndef TGR_INCLUDED
+end module derivs2
+#endif
-- 
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