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diff --git a/module/ffts.m b/module/ffts.m
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+FFTs: module{
+	PATH:	con	"/dis/math/ffts.dis";
+
+	ffts: fn(a,b:array of real, ntot,n,nspan,isn:int);
+};
+
+#  multivariate complex fourier transform, computed in place
+#    using mixed-radix fast fourier transform algorithm.
+#  arrays a and b originally hold the real and imaginary
+#    components of the data, and return the real and
+#    imaginary components of the resulting fourier coefficients.
+#  multivariate data is indexed according to the fortran
+#    array element successor function, without limit
+#    on the number of implied multiple subscripts.
+#    the subroutine is called once for each variate.
+#    the calls for a multivariate transform may be in any order.
+#  ntot is the total number of complex data values.
+#  n is the dimension of the current variable.
+#  nspan/n is the spacing of consecutive data values
+#    while indexing the current variable.
+#  the sign of isn determines the sign of the complex
+#    exponential, and the magnitude of isn is normally one.
+#  univariate transform:
+#      ffts(a,b,n,n,n,1)
+#  trivariate transform with a(n1,n2,n3), b(n1,n2,n3):
+#      ffts(a,b,n1*n2*n3,n1,n1,1)
+#      ffts(a,b,n1*n2*n3,n2,n1*n2,1)
+#      ffts(a,b,n1*n2*n3,n3,n1*n2*n3,1)
+#  the data can alternatively be stored in a single vector c
+#    alternating real and imaginary parts. the magnitude of isn changed
+#    to two to give correct indexing increment, and a[0:] and a[1:] used
+#    for a and b