Afegir sessió 3 del lab de fenòmens

Change-Id: Ic21d679decc844e3c2899d6da4cca48301dbae0c
diff --git a/quad10/fenomens/lab/p3/magne.f90 b/quad10/fenomens/lab/p3/magne.f90
new file mode 100644
index 0000000..0e7df92
--- /dev/null
+++ b/quad10/fenomens/lab/p3/magne.f90
@@ -0,0 +1,17 @@
+real*8 function MAGNE(S, L)
+  implicit none
+  integer*4, intent(in) :: L
+  integer*2, intent(out) :: S(1:L,1:L)
+  integer*4 :: i, j
+  real*8 :: mag
+  mag = 0d0
+
+  do i = 1, L
+    do j = 1, L
+      mag = mag + S(i, j)
+    enddo
+  enddo
+
+  magne = mag
+  return
+end function MAGNE