if vm is zero to 0 on input, initialize to abs(xu-xl)

Author: jacobwilliams

src/simulated_annealing.F90

@@ -577,8 +577,9 @@ subroutine sa(me, x, rt, t, vm, xopt, fopt, nacc, nfcnev, ier)
                                                            !! interest given the starting value x.  for point x(i), the next
                                                            !! trial point is selected is from x(i) - vm(i)  to  x(i) + vm(i).
                                                            !! since vm is adjusted so that about half of all points are accepted,
-                                                           !! the input value is not very important (i.e. is the value is off,
+                                                           !! the input value is not very important (i.e. if the value is off,
                                                            !! sa adjusts vm to the correct value).
+                                                           !! note: if `vm=0.0`, then it is set to abs(xu-xl)`.
       real(wp), dimension(me%n), intent(out)  :: xopt      !! the variables that optimize the function.
       real(wp), intent(out)                   :: fopt      !! the optimal value of the function.
       integer, intent(out)                    :: nacc      !! the number of accepted function evaluations.
@@ -629,6 +630,9 @@ subroutine sa(me, x, rt, t, vm, xopt, fopt, nacc, nfcnev, ier)
       xopt        = x
       fopt        = huge(1.0_wp)
       vm          = abs(vm)
+      where (vm == 0.0_wp)
+         vm = abs(me%ub - me%lb)
+      end where
       t_original  = t
       vm_original = vm
       abort       = .false.