code: def read_bvec_file(filename, atol=0.001):
      """
      Read gradient table information from a pair of files with extensions
      .bvec and .bval. The bval file should have one row of values
      representing the bvalues of each volume in the dwi data set. The bvec
      file should have three rows, where the rows are the x, y, and z
      components of the normalized gradient direction for each of the
      volumes.
  
      Parameters
      ----------
      filename :
          The path to the either the bvec or bval file
      atol : float, optional
          The tolerance used to check all the gradient directions are
          normalized. Default is .001
  
      """
  
      base, ext = splitext(filename)
      if ext == "":
          bvec = base + ".bvec"
          bval = base + ".bval"
      elif ext == ".bvec":
          bvec = filename
          bval = base + ".bval"
      elif ext == ".bval":
          bvec = base + ".bvec"
          bval = filename
      else:
          raise ValueError(
              "filename must have .bvec or .bval extension"
          )
  
      b_values = np.loadtxt(bval)
      grad_table = np.loadtxt(bvec)
      if grad_table.shape[0] != 3:
          raise OSError("bvec file should have three rows")
      if b_values.ndim != 1:
          raise OSError("bval file should have one row")
      if b_values.shape[0] != grad_table.shape[1]:
          raise OSError(
              "the gradient file and b value file should"
              "have the same number of columns"
          )
  
      grad_norms = np.sqrt((grad_table**2).sum(0))
      if not np.allclose(grad_norms[b_values > 0], 1, atol=atol):
          raise OSError(
              "the magnitudes of the gradient directions"
              + "are not within "
              + str(atol)
              + " of 1"
          )
      grad_table[:, b_values > 0] = (
          grad_table[:, b_values > 0] / grad_norms[b_values > 0]
      )
  
      return grad_table, b_values
  
file_path: dipy/dipy/io/bvectxt.py
imports: from os.path import splitext
  import numpy
  from dipy.core import gradients
  from dipy.utils.deprecator import deprecate_with_version
label_desc: Use image node_id 1 for calling a global function with example usage: read_bvec_file(filename, atol) and returns: grad_table,  b_values