c
c Convolution.f compiles with g77 on Mac OS X 10.5.8
c
c Example of a convolution ... Running Mean Filter
c Sept.-10, 2013 for MAST-811 in 2013 at UDel
c
	real t(1000),x(1000),xfil(1000),h(1000)
c
c Input data is NAO index from 1950-present
c
	open (unit=7, file='tem')
	n = 756
	do 1 i=1,n
	   read(7,*)t(i),x(i)
1	continue
	write(6,*)t(1),x(1)
	write(6,*)t(n),x(n)
c
c Define the filter-weights (infinity is iww2=12)
c
	iww2 = 12
	h0 = 1./(2.*iww2+1)
	do 4 lag=1,iww2
	   h(lag) = 1./(2.*iww2+1)
4	continue
c
c CONVOLUTION
c
	do 3 i=iww2,n-iww2
	   xfil(i) = x(i)*h0
c
c Evaluate the "integral"
c
	   do 2 lag=1,iww2
c ---->
		xfil(i) = xfil(i)+x(i+lag)*h(lag)+x(i-lag)*h(lag)
c ---->
2	   continue
	   xfil(i) = xfil(i)
	   write(18,*)t(i),x(i),xfil(i)
3	continue
	stop
	end