Perhaps you should try some spelling variations:
"modified stochastic optimization algorithm" » "modified stochastic optimization algorithms", "modified stochastic optimisation algorithm", "modified stochastic estimation algorithm"
"modified average approximation algorithms" » "modified coverage approximation algorithms"

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified average approximation algorithms\") OR (\"modified stochastic optimization algorithm\"))~".
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