Changes between Version 7 and Version 8 of DevelopmentPage/CutTools

Timestamp:

Mar 4, 2010, 10:17:21 AM (14 years ago)

Author:

Rikkert

Comment:

--

DevelopmentPage/CutTools

@@ -42 +42 @@
 What characterizes a loop for CutTools is only a set of momenta and masses for the loop lines. It is then possible to call CutTools with loop amplitudes computed with the sum of the matching color-ordered structures attached to the loop instead of calling CutTools for each structure within this sum.
 This might bring a very significant improvement for large multiplicities processes and small loops, for which there are many color ordered substructures contributing to the same structure attached to the loop. Recognizing these matching structures and organizing the computation with smart calls to CutTools is not straight-forward and will only be implemented in a second stage as an optimization update. But keep in mind that for each loop computation, CutTools calls the cut-diagram amplitude up to 20 times so it is worth trying to spare any single call to CutTools.
+
+
+== More involved optimizations ==
+
+These are some more involved optimizations. It's not yet clear if they are possible to implement and/or if they are really needed.
+
+=== 1) Quadruple (or higher) precision ===
+
+For some phase-space points, normal double precision is not good enough to reliable calculate the value of the loops. CutTools automatically recognizes these points and has the possibility to go to quadruple or higher precision. To do this consistently also the inputs, ie. the HELAS routines should be in higher precision. In fact, only the subroutines that deal with the complex particles need quadruple precision, if the rest is not recomputed for a slightly different value of the q-momenta. So this can only be done after the above optimizations of the FD-structures is implemented.
+
+=== 2) R2 and FD-structures ===
+
+Maybe it's possible to reuse the same FD-structures defined above when calculating the R2 terms or the UV-counterterms. I am not sure it's worth investigating, as I do not expect a big gain here.