[MMTK] Creation of a protein from a sequence

[Konrad Hinsen]

> I am trying to create a protein by specifying the chain sequence and the
> position of the center of mass. I am using the following commands

What do you expect as a result? With only the sequence but no
configuration, all atom positions are necessarily undefined. There is
no way to define the center of mass without having atom positions.

> in centerOfMass
>     mr = mr + a._mass * a.position(conf)
> TypeError: number coercion failed

a.position(conf) will return None, meaning "undefined position".
The attempt to multiply None by the mass causes the error.

Konrad.
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