Columbia subject headings:
Boundary value problems--Numerical solutions.
Differential operators.
Perturbation (Mathematics)
Spectral theory (Mathematics)
Harvard subject headings:
Boundary value problems--Numerical solutions.
Differential operators.
Perturbation (Mathematics)
Spectral theory (Mathematics)
Princeton subject headings:
Boundary value problems--Numerical solutions.
Differential operators.
Perturbation (Mathematics)
Spectral theory (Mathematics)