There is no officiially agreed convention, nor can there really be one. Don't expect the author to have used the same conventions that you personally like to use. Any "convention" like this is purely based on personal perference and who you learned it from. Someone from a different country or background can easily think differently, and they would be just as validly correct as you.
Should it be (r,theta) or (theta,r)? Make sure that you know which was used. Make sure that you know if the software uses radians or degrees for the angle.
When using ANY software, read the help. If you don't, then expect to get random results.