public double d ( double x ) { int intervalNumber = getIntervalNumber ( x ) ; if ( intervalNumber == 0 || intervalNumber == points . length ) { return x ; } return getIntervalReferencePoint ( intervalNumber - 1 ) ; }
If a given x is into an interval of the partition this method returns the reference point of the corresponding interval . If the given x is not contained in any interval of the partition this method returns x .