[cmsdy] in dsample.f of pp_dy3j.mad P0_gux_taptamggux, simplify the c…

…ode for xbin_min and xbin_max (part1 of madgraph5#969)

There is indeed a small but clear improvement

CUDACPP_RUNTIME_DISABLEFPE=1 ./build.cuda_d_inl0_hrd0/madevent_cuda < /tmp/avalassi/input_dy3j_x1_cudacpp
 [COUNTERS] PROGRAM TOTAL                         :    4.5494s
 [COUNTERS] Fortran Other                  (  0 ) :    0.1688s
 [COUNTERS] Fortran Initialise(I/O)        (  1 ) :    0.0669s
 [COUNTERS] Fortran Random2Momenta         (  3 ) :    3.2830s for  1170103 events => throughput is 2.81E-06 events/s
 [COUNTERS] Fortran PDFs                   (  4 ) :    0.1061s for    49152 events => throughput is 2.16E-06 events/s
 [COUNTERS] Fortran UpdateScaleCouplings   (  5 ) :    0.1361s for    16384 events => throughput is 8.31E-06 events/s
 [COUNTERS] Fortran Reweight               (  6 ) :    0.0519s for    16384 events => throughput is 3.17E-06 events/s
 [COUNTERS] Fortran Unweight(LHE-I/O)      (  7 ) :    0.0649s for    16384 events => throughput is 3.96E-06 events/s
 [COUNTERS] Fortran SamplePutPoint         (  8 ) :    0.1366s for  1170103 events => throughput is 1.17E-07 events/s
 [COUNTERS] CudaCpp Initialise             ( 11 ) :    0.4745s
 [COUNTERS] CudaCpp Finalise               ( 12 ) :    0.0257s
 [COUNTERS] CudaCpp MEs                    ( 19 ) :    0.0349s for    16384 events => throughput is 2.13E-06 events/s
 [COUNTERS] OVERALL NON-MEs                ( 21 ) :    4.5145s
 [COUNTERS] OVERALL MEs                    ( 22 ) :    0.0349s for    16384 events => throughput is 2.13E-06 events/s

epochX/cudacpp/pp_dy3j.mad/Source/dsample.f

@@ -1307,8 +1307,7 @@ subroutine sample_get_x(wgt, x, j, ipole, xmin, xmax)
 c            write(*,'(a,4e15.4)') 'Bad limits',xbin_min,xbin_max,
 c     &           xmin,xmax
 c            xbin_max=xbin_min+1d-10
-            xbin_max = xbin(xmax,minvar(j,ipole))
-            xbin_min = min(xbin(xmin,minvar(j,ipole)), xbin_max)
+            xbin_min = min(xbin_min, xbin_max)
          endif
 c
 c     Line which allows us to keep choosing same x