# poliastro.core.util¶

## Module Contents¶

### Functions¶

 eccentricity_vector(k, r, v) circular_velocity(k, a) Compute circular velocity for a given body given thegravitational parameter and the semimajor axis. rotation_matrix(angle, axis) alinspace(start, stop=None, num=50, endpoint=True) Return increasing, evenly spaced angular values over a specified interval. Compute cartesian coordinates from spherical coordinates (norm, colat, long). This function is vectorized.
poliastro.core.util.eccentricity_vector(k, r, v)
poliastro.core.util.circular_velocity(k, a)

Compute circular velocity for a given body given thegravitational parameter and the semimajor axis.

$v = \sqrt{\frac{\mu}{a}}$
Parameters
• k (float) – Gravitational Parameter

• a (float) – Semimajor Axis

poliastro.core.util.rotation_matrix(angle, axis)
poliastro.core.util.alinspace(start, stop=None, num=50, endpoint=True)

Return increasing, evenly spaced angular values over a specified interval.

poliastro.core.util.spherical_to_cartesian(v)

Compute cartesian coordinates from spherical coordinates (norm, colat, long). This function is vectorized.

$\begin{split}v = norm \cdot \begin{bmatrix} \sin(colat)\cos(long)\\ \sin(colat)\sin(long)\\ \cos(colat)\\ \end{bmatrix}\end{split}$
Parameters

v (np.array) – Spherical coordinates in 3D (norm, colat, long). Angles must be in radians.

Returns

v – Cartesian coordinates (x,y,z)

Return type

np.array