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+c
+c-----------------------------------------------------------------------
+c subroutine: iftasm
+c compute idft for real, antisymmetric, n-point sequence x(m) using
+c n/2-point fft
+c antisymmetric sequence means x(m)=-x(n-m), m=1,...,n/2-1
+c note: index m is sequence index--not fortran index
+c-----------------------------------------------------------------------
+c
+      subroutine iftasm(x, n, y)
+      dimension x(1), y(1)
+c
+c x = imaginary array which on input contains the n/2+1 real points of
+c     the transform of the input--i.e. the zero valued real parts
+c     are not given as input
+c     on output x contains the n/2 points of the time sequence
+c     (antisymmetrical)
+c n = true size of input
+c y = scratch array of size n/2+2
+c
+c
+c for n = 2, assume x(1)=0, x(2)=0
+c
+      if (n.gt.2) go to 10
+      x(1) = 0
+      x(2) = 0
+      return
+  10  twopi = 8.*atan(1.0)
+c
+c first compute x1=x(1) term directly
+c use recursion on the sine cosine terms
+c
+      no2 = n/2
+      no4 = n/4
+      tpn = twopi/float(n)
+c
+c scramble original dft (x(k)) to give y(k)
+c use recursion relation to give sin(tpn*i) multiplier
+c
+      cosi = cos(tpn)
+      sini = sin(tpn)
+      cosd = cosi
+      sind = sini
+      nind = no4 + 1
+      do 20 i=2,nind
+        ind = 2*i
+        ind1 = no2 + 2 - i
+        ak = (x(i)-x(ind1))/2.
+        bk = -(x(i)+x(ind1))
+        y(ind) = ak
+        y(ind-1) = bk*sini
+        temp = cosi*cosd - sini*sind
+        sini = cosi*sind + sini*cosd
+        cosi = temp
+  20  continue
+      y(1) = 0.
+      y(2) = 0.
+c
+c take n/2 point idft of y
+c
+      call fsst(y, no2)
+c
+c form x sequence from y sequence
+c
+      x(2) = y(1)/2.
+      x(1) = 0.
+      if (n.eq.4) go to 40
+      do 30 i=2,no4
+        ind = 2*i
+        ind1 = no2 + 2 - i
+        x(ind-1) = (y(i)-y(ind1))/2.
+        t1 = (y(i)+y(ind1))/2.
+        x(ind) = t1 + x(ind-2)
+  30  continue
+  40  x(no2) = -y(no4+1)/2.
+      return
+      end