@article{PORMA_1981__40_1_115442,
     author = {Namasivayam, S. and Ortiz, Eduardo L.},
     title = {Best approximation and the numerical solution of partial differential equations with the tau method},
     journal = {Portugaliae mathematica},
     pages = {97--119},
     publisher = {mathdoc},
     volume = {40},
     number = {1},
     year = {1981},
     mrnumber = {0796092},
     zbl = {0563.65061},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1981__40_1_115442/}
}