\chi^2 calculations

Image plane optimization

With option forme < 0, Lenstool performs image plane optimization. These calculations are done in parallel with OpenMP. However, allowing a large number of CPUs not necessarily increases the efficiency of the calculations. Managing the multithreading might take more time than doing the calculations themselves.

Here is a little benchmark (thanks to Benjamin Clement), that tells us how Lenstool scales up with the number of images per system.

For instance, with 2 systems of 2 images each, Lenstool effectively uses 2 CPUs. Here are some other examples:

• Sum of images per system = Total number of images ==> CPUs effectively used

• 2+2 = 4 => 2

• 2+3 = 6 => 2

• 3+3 = 8 => 3

• 4+3 = 10 => 3

• 4+3+2 = 12 => 4