i.atcorr: add BUGS

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@73204 15284696-431f-4ddb-bdfa-cd5b030d7da7

imagery/i.atcorr/BUGS

@@ -0,0 +1,23 @@
+results are not consistent
+==========================
+  results differ between different systems, depending on CPU and compiler
+
+  by now all calculations are done with double precision floating point,
+  but still results are not consistent
+
+  the code base is large, making it difficult to debug
+
+  for debugging, two different systems are needed that create different 
+  results with identical input
+  
+  functions causing problems are
+  compute() in 6s.cpp
+    particularly the loop over response values per wavelength
+  kernel() in computations.cpp
+    input/output array bp is not initialized
+    in the last loop, sbp must be > 0
+    the second last loop after "if(k != ip)" needs a closer look
+  [add more functions here]
+  
+  the code base needs to be compared against the latest 6S code
+    requires comparing fortran with cpp