forst try

GravityField/.gitignore

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+
+essai

GravityField/Makefile

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+#
+# Fortraneries by tTh - Gravity Field
+#
+
+GFOPT = -Wall -Wextra -g -time 
+
+essai:	essai.f90  Makefile
+	gfortran $(GFOPT) $<  -o $@

GravityField/README.md

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+# Gravity Field
+
+Some crude experiments to make fancy picture of a useless gravaity field.
+
+Expect bug party.

GravityField/essai.f90

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+program essai
+  implicit none
+
+  integer                 :: ix, iy
+  real                    :: fx, fy
+  real                    :: foo, bar, maxi, mini
+
+  maxi = 0.0
+  mini = 9e9
+
+  do ix=1, 2000
+    fx = real(ix)
+    do iy=1, 2000
+      fy = real(iy)
+
+      foo = rdist(fx, fy, 222.22, 765.432)
+      bar = gravity(foo, 1337.0)
+
+      maxi = max(maxi, bar)
+      mini = min(mini, bar)
+
+    enddo
+  enddo
+
+  print *, "dist : ", mini, maxi
+
+contains        !------------------------------------------
+
+function gravity(distance, masse)
+  real, intent(in)      :: distance, masse
+  real                  :: gravity
+  real                  :: computed
+
+  if (distance .LT.  0.010) then
+    computed = 0.0
+  else
+    computed = masse / (distance ** 2)
+  endif
+
+  gravity = computed
+
+end function
+
+                !------------------------------------------
+
+function rdist(ax, ay, bx, by)
+  real, intent(in)       :: ax, ay, bx, by
+  real                      :: rdist
+  real                      :: rx, ry
+
+  rx = real(ax-bx)
+  ry = real(ay-by)
+
+  rdist = sqrt( (rx*rx) + (ry*ry) )
+
+end function
+
+
+                !------------------------------------------
+                !------------------------------------------
+
+end program