1. Cannon, J. R., Some numerical results for the solution of the heat equation backwards in time, Numerical
Solutions
of
Nonlinear
Differential
Equations, editted by D. Greenspan, John Wiley and Sons, Inc., New York, 1966.
2. Douglas, Jr., Jr., Approximate harmonic continuation, Atti
del Conyegno
su
le
equazioni
alle
derivate
parziale, Nervi, 25–27 febbraio 1965, Edizioni Cremonese, Roma.
3. ——, Approximate continuation of harmonic and parabolic functions, Numerical Solution
of
Partial
Differential Equations, editted by J. H. Bramble, Academic Press, Inc., New York, 1966.
4. —— The approximate solution of an unstable physical problem subject to constraints, Functional Analysis
and
Optimization, editted by E. R. Caianiello, Academic Press, Inc., New York, 1966.
5. Widder, D. V., Positive temperatures on an infinite rod, Transactions of the American Mathematical Society 55 (1944) 85–95.