class_docstr: A reference frame in classical mechanics.
  
  ReferenceFrame is a class used to represent a reference frame in classical
  mechanics. It has a standard basis of three unit vectors in the frame's
  x, y, and z directions.
  
  It also can have a rotation relative to a parent frame; this rotation is
  defined by a direction cosine matrix relating this frame's basis vectors to
  the parent frame's basis vectors.  It can also have an angular velocity
  vector, defined in another frame.
docstr: Unit dyad of basis Vectors z and y for the ReferenceFrame.
docstr_tok: ["Unit","dyad","of","basis","Vectors","z","and","y","for","the","ReferenceFrame","."]
code: def zy(self):
      """Unit dyad of basis Vectors z and y for the ReferenceFrame."""
      return Vector.outer(self.z, self.y)
  
imports: from sympy import diff, expand, sin, cos, sympify, eye, zeros, ImmutableMatrix, MatrixBase
  from sympy.core.symbol import Symbol
  from sympy.simplify.trigsimp import trigsimp
  from sympy.physics.vector.vector import Vector, _check_vector
  from sympy.utilities.misc import translate
  from warnings import warn
label_desc: Use image node_id 34 for calling the ReferenceFrame obj's underlying member method code with example usage: obj.zy() and returns: Vector