Göttingen Collection of Mathematical Models and Instruments

To the permutability of the differentiation sequence

Model 215

E I 22


The function z=xy(x²-y²)/(x²+y²), and z(0,0) =0. Its second partial derivatives are not permutable at (0,0). Gypsum. Two exemplars in stock.

Photo of a 3D print

Showcase of this model is Case number 41


Schilling, Martin(Hrg.): Catalog mathematischer Modelle, Leipzig(Verlag von Martin Schilling) 1911, 7.Auflage, No.176. p. 136.