Historically, EFLECH is a very old program. I have developed EFLECH between 1980 and 1990. The peak model involved in BGMN was developed inside EFLECH, originally. So, EFLECH was the first program using the fundamental parameter's peak model described on these web pages. But, in contrary to BGMN, EFLECH fits purely peak parameters using the fundamental parameter's peak model. Otherwise, EFLECH is more than a pure peak fit program: EFLECH automatically hacks for peaks. So, you may run EFLECH with no start diagram! Similar to BGMN, EFLECH automatically choses the degree of background polynom. And, subsequently, EFLECH adds peaks, changes peak parameter numbers, deletes peaks, reduces background polynom according to statistic tests. EFLECH delivers a peak listing: a *.par file similar to those delivered by BGMN. But, in addition to BGMN, EFLECH's *.par files include a covariance matrix of all peak parameters. The OUTPUT program shows these error informations in the peak listing.
In 1996, I have started developing INDEX. This indexing program uses the covariance matrix delivered by EFLECH. So, it may handle bad diagrams with low peak quality. INDEX does not use triplets or quartets of peaks. It mostly delivers the best possible solution for indexing. INDEX uses a random search algorithm.
INDEX was optimized for reaching almost the optimum solution of a given pattern. This means, it needs for a fast processor (Pentium 4, Athlon XP+) and a lot of computing time. For a normal laboratory pattern (medium resolution) this means:
For synchrotron data, the situation changes. Optimized to reach every possible solution, INDEX demands for weeks for monoclinic/triclinic systems. But, many synchrotron patterns include magnitudes of overestimation for INDEX (their purpose is common indexing). Therefore, I do not recommend synchrotron data at this point, excepting cases of great unit cell and low symmetry.