Perhaps you should try some spelling variations:
"defined network optimization algorithms" » "defined network optimisation algorithm", "defined network estimation algorithms", "defined network estimation algorithm"
"modified parameter approximation algorithms" » "modified parameters approximation algorithms"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("modified parameter approximation algorithms") or ("defined network optimization algorithms"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified parameter approximation algorithms") OR ("defined network optimization algorithms"))*.
• Removing quotes may allow a broader search: (( modified parameter approximation algorithms ) or ( defined network optimization algorithms ))*.