Perhaps you should try some spelling variations:
"modified allocation approximation algorithms" » "modified allocation optimization algorithms"
"modified parameter estimation algorithms" » "modified parameter estimation algorithm", "modified parameter optimization algorithms", "modified parameter optimisation algorithm", "modified parameter estimates algorithms"

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