Note : The scientific Python ecosystem is changing at a rapid pace, without maintaining compatibility with older versions. Since the beginning of MMTK development in 1996, there have been important changes to the Python language itself between Python and Python 3, and also a large number of smaller incompatible changes to the NumPy library that MMTK depends on. MMTK has not been adapted to these changes, because we do not have sufficient resources for software development. Therefore MMTK can be used only with Python and NumPy , but not with later releases of either software.
A good example of composite models is the Nicholson approach, widely used from the late 1970s for building models of biological macromolecules . The components are primarily amino acids and nucleic acids with preformed residues representing groups of atoms. Many of these atoms are directly moulded into the template, and fit together by pushing plastic stubs into small holes. The plastic grips well and makes bonds difficult to rotate, so that arbitrary torsion angles can be set and retain their value. The conformations of the backbone and side chains are determined by pre-computing the torsion angles and then adjusting the model with a protractor .