code: def test_min_at():
      k = np.array([3, 2, 2, 2, 1, 1, 1])
      values = np.array([10.0, 1, 2, 3, 31, 21, 11])
      i = np.zeros(k.shape, int)
      j = np.zeros(k.shape, int)
      a = np.zeros([1, 1, 4]) + 100.0
  
      _min_at(a, (i, j, k), values)
      npt.assert_array_equal(a, [[[100, 11, 1, 10]]])
  
imports: import warnings
  import numpy
  import pytest
  from dipy.tracking import metrics
  from dipy.tracking.streamline import transform_streamlines
  from dipy.tracking.utils import connectivity_matrix, density_map, length, ndbincount, reduce_labels, seeds_from_mask, random_seeds_from_mask, target, target_line_based, unique_rows, near_roi, reduce_rois, path_length, _min_at, max_angle_from_curvature, min_radius_curvature_from_angle
  from dipy.tracking._utils import _to_voxel_coordinates
  from dipy.tracking.vox2track import streamline_mapping
  import numpy.testing
  from dipy.testing import assert_true
  from dipy.testing.decorators import set_random_number_generator
label_desc: Use image node_id 20 for calling a global function with example usage: test_min_at() without return types