On a Liouville transformation for $u_{xx} + u_{yy} \pm a^{2}(x,y)u=0$.
Bollettino della Unione matematica italiana, Série 3, Tome 13 (1958) no. 4, pp. 535-538
@article{BUMI_1958_3_13_4_a9,
author = {Bellman, Richard},
title = {On a {Liouville} transformation for $u_{xx} + u_{yy} \pm a^{2}(x,y)u=0$.},
journal = {Bollettino della Unione matematica italiana},
pages = {535--538},
year = {1958},
volume = {Ser. 3, 13},
number = {4},
zbl = {0087.09601},
mrnumber = {100712},
language = {en},
url = {http://geodesic.mathdoc.fr/item/BUMI_1958_3_13_4_a9/}
}
Bellman, Richard. On a Liouville transformation for $u_{xx} + u_{yy} \pm a^{2}(x,y)u=0$.. Bollettino della Unione matematica italiana, Série 3, Tome 13 (1958) no. 4, pp. 535-538. http://geodesic.mathdoc.fr/item/BUMI_1958_3_13_4_a9/