first dry run

GravityField/realfield.f90

@@ -0,0 +1,42 @@
+!
+!       project "gravity field"
+!
+!-----------------------------------------------------------------------
+module realfield
+  implicit none
+
+!-----------------------------------------------------------------------
+
+type massbody
+  real                  :: posx, posy
+  real                  :: mass
+  integer               :: serial
+end type
+
+!-----------------------------------------------------------------------
+contains
+
+function compute_gravity(ix, iy, body)
+
+  integer, intent(in)           :: ix, iy
+  type(massbody), intent(in)    :: body
+  real                          :: compute_gravity
+  real                           :: rx, ry, dist
+
+  rx = real(ix) - body%posx
+  ry = real(iy) - body%posy
+
+  dist = sqrt( (rx*rx) + (ry*ry) )
+  if (dist .LT. 0.15) then
+    write (0, *) "dist too small ", dist
+    compute_gravity = 0e0
+  endif
+
+  compute_gravity = body%mass * (dist ** 2)
+
+end function
+
+!-----------------------------------------------------------------------
+!-----------------------------------------------------------------------
+
+end module