diff --git a/code/m_calculate.f90 b/code/m_calculate.f90
index e2e7519..b1ef3f9 100644
--- a/code/m_calculate.f90
+++ b/code/m_calculate.f90
@@ -252,4 +252,28 @@ contains
 
      end function threshold_min_max
 
+     real function positive (c)
+
+      real :: c
+
+        if (c > 0.0d0) then
+            positive = c
+        else
+            positive = 0.
+        end if
+
+     end function positive
+
+     real function negative (c)
+
+      real :: c
+
+        if (c < 0.0d0) then
+            negative = c
+        else
+            negative = 0.
+        end if
+
+     end function negative
+
 end module m_calculate