/*
 *  call-seq:
 *     dvector.trim(cutoff=1e-6)   ->  a_dvector
 *  
 *  Returns a copy of _dvector_ with any entry with absolute value less than _cutoff_ replaced by 0.
 *     
 *     a = Dvector[ 1.1, 1e-20, -5.3 ]
 *     a.trim  -> Dvector[ 1.1, 0, -5.3 ]
 */ 
VALUE dvector_trim(int argc, VALUE *argv, VALUE self) {