[R] need help with smooth.spline

[W. C. Thacker]

Dear R listers,

When using smooth.spline to interpolate data, results are generally
good.  However, some cases produce totally unreasonable results.

The data are values of pressure, temperature, and salinity from a
probe that is lowered into the ocean, and the objective is to
interpolate temperature and salinity to specified pressures.  While
smooth.spline provides excellent values at the observed pressures,
there are cases when the values at the desired pressures are
unusable.  A dataframe with four such profiles, indicated by values of
id, is attached.  My target values for pressure are seq(25,1600,25),
but 1:500 is also interesting.  

Setting all.knots = TRUE helps, but it would be nice to be able to do
better.

Any suggestions?

Thanks,

Carlisle

> version
         _                   
platform sparc-sun-solaris2.9
arch     sparc               
os       solaris2.9          
system   sparc, solaris2.9   
status                       
major    1                   
minor    8.0                 
year     2003                
month    10                  
day      08                  
language R                   


-- 

William Carlisle Thacker                            
                                                    
Atlantic Oceanographic and Meteorological Laboratory
4301 Rickenbacker Causeway, Miami, Florida 33149 USA
Office: (305) 361-4323           Fax: (305) 361-4392

"Too many have dispensed with generosity 
     in order to practice charity."     Albert Camus