code: def _trace(x):
      """
      Trace of a square 2d array.
  
      Does not check
      shape of x to ensure it's square.
      """
      return np.diag(x).sum()
  
imports: import numpy
  from numpy.linalg import svd
  from .reml import orth
label_desc: Use image node_id 1 for calling a global function with example usage: _trace(x) and returns: np