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subroutine desi11(nmaxi,maxdeg,vsn,ndeg,gd1,gd2,adelta,nzm,sm
*,nzero,pren,pimn,ugc,ogc,nj,nh)
c!purpose
c butterworth filter
c computation of the zeros and locations of the extrema
c!
c
implicit double precision (a-h,o-z)
external slamch
real slamch
dimension nzm(*),sm(maxdeg,4),nzero(*),pren(*),pimn(*)
c
pi=4.0d+0*atan(1.0d+0)
flma=2.0d+0**(int(slamch('l'))-2)
c
adelta = vsn**ndeg
c
nh = ndeg/2
nj = (ndeg+1)/2
fdeg = real(ndeg)
fn = pi/2.0d+0/fdeg
c
do 10 i=1,nj
nzero(i) = 0
iii = i + i - 1
q = fn*real(iii)
pren(i) = sin(q)
pimn(i) = cos(q)
10 continue
c
fn = 2.0d+0*fn
nzero(1) = ndeg
nzm(1) = 1
sm(1,1) = 0.0d+0
nzm(2) = 1
sm(1,2) = 1.0d+0
nzm(3) = 1
sm(1,3) = vsn
nzm(4) = 1
sm(1,4) = flma
c
ugc = gd2/adelta
ogc = gd1
sm(nmaxi-1,4) = 1.0d+0
return
end
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