Perhaps you should try some spelling variations:
"modified df optimization algorithm" » "modified df optimization algorithms", "modified df optimisation algorithm", "modified df estimation algorithm", "modified _ optimization algorithm", "modified qoe optimization algorithm", "modified _ optimisation algorithm", "modified adam optimization algorithm", "modified bi1 optimization algorithm"
"modified objective optimization algorithm" » "modified objective optimization algorithms", "modified objective optimisation algorithm", "modified objective estimation algorithm", "modified multiobjective optimization algorithm"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified df optimization algorithm") OR ("modified objective optimization algorithm"))~.
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