ATLAS uses a BSD-style license for its distribution, and thus any code that you wish to contribute must have a compatible license. This effectively rules out GPL and even LGPL licenses, since if the ATLAS group redistributed any routines with these licenses, the conditions of their licenses would effectively change the entire ATLAS library to GPL or LGPL.
Note that you, the author, retain the copyright, and thus you can relicense your code in any way you wish. So, anything released as part of the ATLAS tarfile will need a BSD-compatible license, but you could then issue the code yourself under a different license. Alternatively, you can provide your codes as ``patches'' to standard ATLAS, and thus avoid the license issue altogether, at the cost of not being part of the standard tarfile. Even if you decide not to license your contribution in a way that the ATLAS group can redistribute, submitting it to the mailing list is still recommended. Other people can see your work, and we can point to it if we think it is cool enough.
Clint Whaley 2012-07-10