# 3ddot¶

```
Usage: 3ddot [options] dset1 [dset2 dset3 ...]
Output = correlation coefficient between sub-brick pairs
All datasets on the command line will get catenated
at loading time and should all be on the same grid.
- you can use sub-brick selectors on the dsets
- the result is a number printed to stdout
Options:
-mask mset Means to use the dataset 'mset' as a mask:
Only voxels with nonzero values in 'mset'
will be averaged from 'dataset'. Note
that the mask dataset and the input dataset
must have the same number of voxels.
-mrange a b Means to further restrict the voxels from
'mset' so that only those mask values
between 'a' and 'b' (inclusive) will
be used. If this option is not given,
all nonzero values from 'mset' are used.
Note that if a voxel is zero in 'mset', then
it won't be included, even if a < 0 < b.
-demean Means to remove the mean from each volume
prior to computing the correlation.
-docor Return the correlation coefficient (default).
-dodot Return the dot product (unscaled).
-docoef Return the least square fit coefficients
{a,b} so that dset2 is approximately a + b*dset1
-dosums Return the 6 numbers xbar=<x> ybar=<y>
<(x-xbar)^2> <(y-ybar)^2> <(x-xbar)(y-ybar)>
and the correlation coefficient.
-doeta2 Return eta-squared (Cohen, NeuroImage 2008).
-dodice Return the Dice coefficient (the Sorensen-Dice index).
-show_labels Print sub-brick labels to help identify what
is being correlated. This option is useful when
you have more than 2 sub-bricks at input.
-upper Compute upper triangular matrix
-full Compute the whole matrix. A waste of time, but handy
for parsing.
-1D Comment headings in order to read in 1D format.
This is only useful with -full.
-NIML Write output in NIML 1D format. Nicer for plotting.
-full and -show_labels are automatically turned on with -NIML.
For example:
3ddot -NIML anat.001.sc7z.sigset+orig"[0,1,2,3,4]" \
> corrmat.1D
1dRplot corrmat.1D
or
1dRplot -save somecorr.jpg -i corrmat.1D
Note: This program is not efficient when more than two subbricks are input.
INPUT DATASET NAMES
-------------------
This program accepts datasets that are modified on input according to the
following schemes:
'r1+orig[3..5]' {sub-brick selector}
'r1+orig<100..200>' {sub-range selector}
'r1+orig[3..5]<100..200>' {both selectors}
'3dcalc( -a r1+orig -b r2+orig -expr 0.5*(a+b) )' {calculation}
For the gruesome details, see the output of 'afni -help'.
++ Compile date = Sep 1 2021 {AFNI_21.2.06:linux_ubuntu_16_64}
```