Perhaps you should try some spelling variations:
optimization algorithms » optimisation algorithm, estimation algorithms, estimation algorithm
approximation algorithm » approximation algorithms
df approximation » _ approximation, one approximation, time approximation
modified df » modified _, modified adam, modified bi1
defined » designed

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "(( defined network optimization algorithms ) OR ( modified df approximation algorithm ))~".
• Adding a wildcard symbol may retrieve word variants: (( defined network optimization algorithms ) OR ( modified df approximation algorithm ))*.