diff --git a/gpl_module.f90 b/gpl_module.f90
index d979e539640804362081207358dd1ad0e7245c03..8eca5bbae630e5fb919fe768ac4902d9f0652bab 100644
--- a/gpl_module.f90
+++ b/gpl_module.f90
@@ -1,4 +1,4 @@
- 
+
 MODULE gpl_module
   use mpl_module
 
@@ -6,12 +6,38 @@ MODULE gpl_module
 
 CONTAINS 
 
-  FUNCTION GPL()
-    ! integer :: m(:)
-    ! complex(kind=prec) :: y(:)
-    complex(kind=prec) GPL
+  FUNCTION GPL(m,z,y,k)
+    ! computes the generalized polylogarithm G_{m1,..mk} (z1,...zk; y)
+
+    integer :: m(:), k, i
+    complex(kind=prec) :: z(:), x(k), y, GPL
+
+    ! print*, 'GPL called with arguments:'
+    ! print*, 'm=',m
+    ! print*, 'z=',z
+    ! print*, 'y=',y
+
+    do i = 1,k
+      x(i) = merge(y/z(1), z(i-1)/z(i),i == 1)
+    end do
+
+    GPL = (-1)**k * MPL(m,x)
 
-    print*, 'hello, GPL'
   END FUNCTION GPL
 
 END MODULE gpl_module
+
+! PROGRAM test
+!   ! used to test this module
+!   use gpl_module
+  
+!   integer :: m(2) = (/ 1,1 /)
+!   complex(kind=prec) :: z(2) = dcmplx((/ 1.3d0, 1.1d0 /))
+!   complex(kind=prec) :: y = 0.4
+!   complex(kind=prec) :: res
+  
+!   res = GPL(m,z,y,2)
+!   print*, 'res=',res
+
+! END PROGRAM test
+
diff --git a/test.f90 b/test.f90
index 6efe95e1130d15ec2e8901196bb4c0197036bd2e..860ac3df04c7058701085aac912a6effa7241988 100644
--- a/test.f90
+++ b/test.f90
@@ -12,8 +12,6 @@ PROGRAM TEST
 
   call do_MPL_tests() 
 
-  res = GPL()
-
 CONTAINS
   
   subroutine do_MPL_tests()
@@ -25,18 +23,18 @@ CONTAINS
     print*, 'doing multiple polylog tests...'
     
     m2 = (/ 1,1 /)
-    x2 = cmplx((/ 0.3156498673740053, 0.3431255827785649 /))
-    ref = cmplx(0.022696600480693277651633)
+    x2 = dcmplx((/ 0.3156498673740053, 0.3431255827785649 /))
+    ref = dcmplx(0.022696600480693277651633)
     call check_MPL(m2,x2,ref)
 
     m2 = (/ 1,1 /)
-    x2 = cmplx((/ 0.03, 0.5012562893380046 /))
-    ref = cmplx(0.00023134615630308335448329926098409)
+    x2 = dcmplx((/ 0.03, 0.5012562893380046 /))
+    ref = dcmplx(0.00023134615630308335448329926098409)
     call check_MPL(m2,x2,ref)
     
     m3 = (/ 2,1,2 /)
-    x3 = cmplx((/ 0.03, 0.5012562893380046, 55.3832 /))
-    ref = cmplx(0.000023446106415452030937059124671151)
+    x3 = dcmplx((/ 0.03, 0.5012562893380046, 55.3832 /))
+    ref = dcmplx(0.000023446106415452030937059124671151)
     call check_MPL(m3,x3,ref)
   end subroutine do_MPL_tests