# Bio.PDB.vectors module¶

Vector class, including rotation-related functions.

`Bio.PDB.vectors.``m2rotaxis`(m)

Return angles, axis pair that corresponds to rotation matrix m.

The case where `m` is the identity matrix corresponds to a singularity where any rotation axis is valid. In that case, `Vector([1, 0, 0])`, is returned.

`Bio.PDB.vectors.``vector_to_axis`(line, point)

Vector to axis method.

Return the vector between a point and the closest point on a line (ie. the perpendicular projection of the point on the line).

Parameters
• line (L{Vector}) – vector defining a line

• point (L{Vector}) – vector defining the point

`Bio.PDB.vectors.``rotaxis2m`(theta, vector)

Calculate left multiplying rotation matrix.

Calculate a left multiplying rotation matrix that rotates theta rad around vector.

Parameters
• theta (float) – the rotation angle

• vector (L{Vector}) – the rotation axis

Returns

The rotation matrix, a 3x3 Numeric array.

Examples

```>>> from numpy import pi
>>> from Bio.PDB.vectors import rotaxis2m
>>> from Bio.PDB.vectors import Vector
>>> m = rotaxis2m(pi, Vector(1, 0, 0))
>>> Vector(1, 2, 3).left_multiply(m)
<Vector 1.00, -2.00, -3.00>
```
`Bio.PDB.vectors.``rotaxis`(theta, vector)

Calculate left multiplying rotation matrix.

Calculate a left multiplying rotation matrix that rotates theta rad around vector.

Parameters
• theta (float) – the rotation angle

• vector (L{Vector}) – the rotation axis

Returns

The rotation matrix, a 3x3 Numeric array.

Examples

```>>> from numpy import pi
>>> from Bio.PDB.vectors import rotaxis2m
>>> from Bio.PDB.vectors import Vector
>>> m = rotaxis2m(pi, Vector(1, 0, 0))
>>> Vector(1, 2, 3).left_multiply(m)
<Vector 1.00, -2.00, -3.00>
```
`Bio.PDB.vectors.``refmat`(p, q)

Return a (left multiplying) matrix that mirrors p onto q.

Returns

The mirror operation, a 3x3 Numeric array.

Examples

```>>> from Bio.PDB.vectors import refmat
>>> p, q = Vector(1, 2, 3), Vector(2, 3, 5)
>>> mirror = refmat(p, q)
>>> qq = p.left_multiply(mirror)
>>> print(q)
<Vector 2.00, 3.00, 5.00>
>>> print(qq)
<Vector 1.21, 1.82, 3.03>
```
`Bio.PDB.vectors.``rotmat`(p, q)

Return a (left multiplying) matrix that rotates p onto q.

Parameters
• p (L{Vector}) – moving vector

• q (L{Vector}) – fixed vector

Returns

rotation matrix that rotates p onto q

Return type

3x3 Numeric array

Examples

```>>> from Bio.PDB.vectors import rotmat
>>> p, q = Vector(1, 2, 3), Vector(2, 3, 5)
>>> r = rotmat(p, q)
>>> print(q)
<Vector 2.00, 3.00, 5.00>
>>> print(p)
<Vector 1.00, 2.00, 3.00>
>>> p.left_multiply(r)
<Vector 1.21, 1.82, 3.03>
```
`Bio.PDB.vectors.``calc_angle`(v1, v2, v3)

Calculate angle method.

Calculate the angle between 3 vectors representing 3 connected points.

Parameters

v2, v3 (v1,) – the tree points that define the angle

Returns

angle

Return type

float

`Bio.PDB.vectors.``calc_dihedral`(v1, v2, v3, v4)

Calculate dihedral angle method.

Calculate the dihedral angle between 4 vectors representing 4 connected points. The angle is in ]-pi, pi].

Parameters

v2, v3, v4 (v1,) – the four points that define the dihedral angle

class `Bio.PDB.vectors.``Vector`(x, y=None, z=None)

Bases: `object`

3D vector.

`__init__`(self, x, y=None, z=None)

Initialize the class.

`__repr__`(self)

Return vector 3D coordinates.

`__neg__`(self)

Return Vector(-x, -y, -z).

`__add__`(self, other)

Return Vector+other Vector or scalar.

`__sub__`(self, other)

Return Vector-other Vector or scalar.

`__mul__`(self, other)

Return Vector.Vector (dot product).

`__truediv__`(self, x)

Return Vector(coords/a).

`__div__`(self, x)

Return Vector(coords/a).

`__pow__`(self, other)

Return VectorxVector (cross product) or Vectorxscalar.

`__getitem__`(self, i)

Return value of array index i.

`__setitem__`(self, i, value)

Assign values to array index i.

`__contains__`(self, i)

Validate if i is in array.

`norm`(self)

Return vector norm.

`normsq`(self)

Return square of vector norm.

`normalize`(self)

Normalize the Vector object.

Changes the state of `self` and doesn’t return a value. If you need to chain function calls or create a new object use the `normalized` method.

`normalized`(self)

Return a normalized copy of the Vector.

To avoid allocating new objects use the `normalize` method.

`angle`(self, other)

Return angle between two vectors.

`get_array`(self)

Return (a copy of) the array of coordinates.

`left_multiply`(self, matrix)

Return Vector=Matrix x Vector.

`right_multiply`(self, matrix)

Return Vector=Vector x Matrix.

`copy`(self)

Return a deep copy of the Vector.