code: def read_double_matrix(fid, rows, cols):
      """Read 64bit float matrix from bti file."""
      return _unpack_matrix(
          fid, rows, cols, dtype=">f8", out_dtype=np.float64
      )
  
imports: import numpy
  from ..._fiff.utils import read_str
label_desc: Use image node_id 17 for calling a global function with example usage: read_double_matrix(fid, rows, cols) and returns: _unpack_matrix