Svetz's thumb was on the direction vector, pushing hard enough to break it Up, up, up.

The last two lines follow from the cases when the direction vector is parallel to the halfplane defined by the row of : .

Their direction vectors are the principal directions or eigenvectors.

There are multiple published approaches to using a history of updates to form this direction vector.

The curve passes through all its control points (Cα atoms) guided by direction vectors.

The ray's source may be a point (called the radiant) or infinity, in which case a direction vector must be specified.

Then one direction vector of is .

Any multiple of is also a direction vector.

Then , , and are all direction vectors for this line.

This line has v as a direction vector.