/usr/share/gretl/scripts/misc/convolve.inp is in gretl-common 1.9.6-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 | # define two polynomials
a = { 1, 0.5, 0, 0 }'
b = { 1, 0.3, -0.8, 0 }'
# perform the transforms
f = fft(a ~ b)
# complex-multiply the two transforms
fc = cmult(f[,1:2], f[,3:4])
print fc
# compute the coefficients of c = a * b via the inverse transform
c = ffti(fc)
print c
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