Howdy-

We (= me) has been slow to update the AFNI install instructions for Ubuntu 20.04. Thanks for information on this.

I have just taken an old laptop and installed Ubuntu 20.04, and am going through the setup. I will hopefully put up a full doc page by Monday (or so) about this, but some things to note:

A) Re. python-matplotlib (this is separate from the "xfonts-base" part, which is fine in the current documentation):
Ubuntu and its repo will now look for Python 3 specifically (because Python 2 became deprecated in Dec, 2019). If you search for matplotlib in the aptitude repo:

apt-cache search matplotlib

... it won't have "python-matplotlib" anymore (which was python 2's matplotlib module), but instead it will have "python3-matplotlib"
All this is to say, you can run:

sudo apt-get install -y python3-matplotlib

and that will get you Python 3 + matplotlib; and I think numpy will also be there as well, it appears, which might soon become an AFNI depedency.

Also, even more preferably for managing Python, I have gotten to like Conda/Miniconda, and find it pretty convenient overall to manage various python setups and install packages. We have instructions for this now on the AFNI webpages-- it's optional, but might be useful:
[afni.nimh.nih.gov]

B) Re. python-qt4
I believe this is also Python 2.* specific; I don't think you need to worry about this one, and can ignore (we don't really use the qt-based GUIs in AFNI at the moment for anything). There are Python 3 equivalents that one day we might use, but that isn't an immediate thing.

C) Re. lib-gfortran3 (here also, "libssl-dev" is a separate consideration, and one that appears to be correct in the install):
Chris Rorden has kindly done some of our homework for us, and noted this point here:
[github.com]
... so you should be able to do this instead:

sudo apt install libgfortran-8-dev libgomp1

D) Re. R:
Maybe having lib-gfortran-8-dev will help this-- I still have to investigate.

thanks,
pt