Perhaps you should try some spelling variations:
"positive-definiten ersten" » "positive-definition erster", "positive-definition arten", "positive-definite system"
"positive-definiten kernen" » "positive-definite kernels", "positive-definiten formen", "positive-semidefiniten kernen"

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: "((\"positive-definiten ersten\") OR (\"positive-definiten kernen\"))".
• Removing quotes may allow a broader search: (( positive-definiten ersten ) OR ( positive-definiten kernen )).
• Adding a wildcard symbol may retrieve word variants: (("positive-definiten ersten") OR ("positive-definiten kernen"))*.