### Gaussian kernel correlation integral

`c2g [-o `*outfile*` -V# -h] `* file*

` -o `output file name, just ` -o `means *file*`_g`

` -V `verbosity level (0 = only fatal errors)

` -h `show this message

Reads two columns, r, c(r) from *file*
(correlation integral output of
c2naive or
d2 (extension **.c2**)
and computes the Gaussian kernel
correlation integral
/00 2
1 | / x \
C (r) = --- | dx exp |- ----- | x C(x)
G 2 | \ 2 /
r /0 2r

As well as its logarithmic derivative with respect to r:
d
D (r) = ------- log C (r)
G d log r G

**Note:** The length scale has been shifted by
2^{1/2} with respect to the manual: r^{2}=2^{2}.
Between the given values of r, C(r) is interpolated by an exact power law and
the integral is evaluated numerically. Above the largest given value of r,
C(r)=1 is assumed and the corresponding integral is evaluated analytically.
The derivative is carried out analytically on the above expression and the
resulting integral is evaluated in the same manner as described.

Output is to `stdout`, or to
file *file*`_g` if
` -o` is given. The first column contains
r, the second the Gaussian kernel correlation integral C_{G}(r) and
the third its
logarithmic derivative D_{G}(r).

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