@article{IM2_2018_82_6_a2,
     author = {V. A. Klyachin},
     title = {Approximation of the gradient of a~function on the basis of a~special},
     journal = {Izvestiya. Mathematics},
     pages = {1136--1147},
     year = {2018},
     volume = {82},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2018_82_6_a2/}
}