# MDTraj Utils¶

MDTraj contains a number of tools to help with development. These are located in mdtraj.utils.

## Miscellanies¶

 import_(module) Import a module, and issue a nice message to stderr if the module isn’t installed. in_units_of(quantity, units_in, units_out[, …]) Convert a numerical quantity between unit systems. ilen(iterable) Length of an iterator. timing([name]) A timing context manager

## Validation¶

 ensure_type(val, dtype, ndim, name[, …]) Typecheck the size, shape and dtype of a numpy array, with optional casting. Turn seed into a np.random.RandomState instance

## Unit cell and Periodic Boundary Conditions¶

 lengths_and_angles_to_box_vectors(a_length, …) Convert from the lengths/angles of the unit cell to the box vectors (Bravais vectors). Convert box vectors into the lengths and angles defining the box.

## Rotations¶

 Compute a 3x3 rotation matrix from a given quaternion (4-vector). uniform_quaternion([size, random_state]) Generate uniform normalized quaternion 4-vectors