#### Description:

The routine uses the
QUICKSORT algorithm to sort an array of values into descending order. The “median of three”
modification is included to reduce the likelihood of encountering the worst-case behaviour of
QUICKSORT.

The routine exists for types REAL (x=R), DOUBLE PRECISION (x=D), and INTEGER (x=I).

#### Invocation

CALL PDA_QSDx( EL, X )

#### Arguments

##### EL = INTEGER (Given)

The number of
elements of X to be sorted.

##### X( EL ) = TYPE (Given and Returned)

The array to be sorted.

####
References

Sedgwick, R., 1988, Algorithms (Addison-Wesley).

#### Timing

If N elements are to be
sorted, the average time goes as N*ln(N). The worst-case time goes as N**2.

#### Copyright

Copyright
(C) 1992 Science & Engineering Research Council