1. 
   Hodrick-Prescott filter
   Algorithm for choosing smoothed values for a time series. The H-P filter chooses smooth values {s_t} for the series {x_t} of T elements (t=1 to T) that solve the following minimization problem: min { {(x_t-s_t)² ... etc. } Parameter l>0...
   Found op http://www.econterms.com/glossary.cgi?query=Hodrick-Prescott+filter
   
   
2. 
   Hodrick–Prescott filter
   ==Drawbacks to the H–P filter== The Hodrick–Prescott filter will only be optimal{clarify|date=February 2010|reason=hoe define optimal here} when: ...
   Found op http://en.wikipedia.org/wiki/Hodrick–Prescott_filter
   
   

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