[cctbxbb] Assertion Error in twin target test

[Luc Bourhis]

Hi all,

I have modified the least square residual classes in cctbx/xray/ 
targets.h and cctbx.xray to handle refinement against F^2. In the  
subsequent tests, the following assertion failure cropped up. It does  
not feel to me my changes caused it…

Luc

libtbx.python /Users/luc/Developer/cctbx/cctbx_sources/cctbx/cctbx/ 
regression/tst_twin_target.py
approx_equal eps: 0.5
approx_equal multiplier: 10000000000.0
-0.510137170481 approx_equal ERROR
0 approx_equal ERROR

Traceback (most recent call last):
   File "/Users/luc/Developer/cctbx/cctbx_sources/cctbx/cctbx/ 
regression/tst_twin_target.py", line 540, in <module>
     run()
   File "/Users/luc/Developer/cctbx/cctbx_sources/cctbx/cctbx/ 
regression/tst_twin_target.py", line 488, in run
     tst_ls_on_i()
   File "/Users/luc/Developer/cctbx/cctbx_sources/cctbx/cctbx/ 
regression/tst_twin_target.py", line 95, in tst_ls_on_i
     assert approx_equal( (fdif_real-old_derivs[0][N_test])/fdif_real, 
0, eps=5e-1)
AssertionError