diff --git a/quad10/fenomens/lab/p4/energ.f90 b/quad10/fenomens/lab/p4/energ.f90
new file mode 100644
index 0000000..ba7841c
--- /dev/null
+++ b/quad10/fenomens/lab/p4/energ.f90
@@ -0,0 +1,13 @@
+real*8 function ENERG(S, L)
+  integer*2 :: S(1:64, 1:64)
+  integer*4 :: I, J, L, PBC
+  real*8 :: ENE
+  ENE = 0.0d0
+  do I = 1, L
+    do J = 1, L
+      ENE = ENE - S(I, J)*S(PBC(I + 1, L), J) - S(I, J)*S(I, PBC(J + 1, L))
+    enddo
+  enddo
+  ENERG = ENE
+  return
+endfunction