NAG CL Interfacem01dsc (rank_​sort)

Settings help

CL Name Style:

1Purpose

m01dsc ranks a vector of arbitrary data type objects in ascending or descending order.

2Specification

 #include
void  m01dsc (const Pointer vec, size_t n, ptrdiff_t stride,
 Integer (*compare)(const Nag_Pointer a, const Nag_Pointer b),
Nag_SortOrder order, size_t ranks[], NagError *fail)
The function may be called by the names: m01dsc, nag_sort_rank_sort or nag_rank_sort.

3Description

m01dsc ranks a set of $n$ data objects of arbitrary type, which are stored in the elements of an array at intervals of length stride. The ranks are in the range 0 to $n-1$.
Either ascending or descending ranking order may be specified.
m01dsc uses a variant of list merging as described by Knuth (1973).

4References

Knuth D E (1973) The Art of Computer Programming (Volume 3) (2nd Edition) Addison–Wesley

5Arguments

1: $\mathbf{vec}\left[{\mathbf{n}}\right]$const Pointer  Input
On entry: the array of objects to be ranked.
2: $\mathbf{n}$size_t Input
On entry: the number $n$ of objects.
Constraint: $0\le {\mathbf{n}}\le \mathrm{MAX_LENGTH}$, where $\mathrm{MAX_LENGTH}$ is an implementation-dependent value for the maximum size of an array.
3: $\mathbf{stride}$ptrdiff_t Input
On entry: the increment between data items in vec to be ranked.
Note: if stride is positive, vec should point at the first data object; otherwise vec should point at the last data object.
Constraint: $0<|{\mathbf{stride}}|\le p$, where $p$ is an implementation-dependent value for the maximum size_t size on the system, divided by n if n is positive.
4: $\mathbf{compare}$function, supplied by the user External Function
m01dsc compares two data objects. If its arguments are pointers to a structure, this function must allow for the offset of the data field in the structure (if it is not the first).
The function must return:
 $-1$ if the first data field is less than the second, $\phantom{-}0$ if the first data field is equal to the second, $\phantom{-}1$ if the first data field is greater than the second.
The specification of compare is:
 Integer compare (const Nag_Pointer a, const Nag_Pointer b)
1: $\mathbf{a}$const Nag_Pointer  Input
On entry: the first data field.
2: $\mathbf{b}$const Nag_Pointer  Input
On entry: the second data field.
5: $\mathbf{order}$Nag_SortOrder Input
On entry: specifies whether the array is to be ranked into ascending or descending order.
Constraint: ${\mathbf{order}}=\mathrm{Nag_Ascending}$ or $\mathrm{Nag_Descending}$.
6: $\mathbf{ranks}\left[{\mathbf{n}}\right]$size_t Output
On exit: the ranks of the corresponding data elements in vec.
7: $\mathbf{fail}$NagError * Input/Output
The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6Error Indicators and Warnings

On entry, argument order had an illegal value.
NE_INT_ARG_EQ
On entry, ${\mathbf{stride}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{stride}}\ne 0$.
NE_INT_ARG_GT
On entry, ${\mathbf{n}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{n}}\le ⟨\mathit{\text{value}}⟩$, an implementation-dependent size that is printed in the error message.
On entry, ${\mathbf{stride}}=⟨\mathit{\text{value}}⟩$.
Constraint: $|{\mathbf{stride}}|\le ⟨\mathit{\text{value}}⟩$, an implementation-dependent size that is printed in the error message.
NE_INT_ARG_LT
On entry, ${\mathbf{n}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{n}}\ge 0$.

Not applicable.

8Parallelism and Performance

m01dsc is not threaded in any implementation.

The time taken by m01dsc is approximately proportional to $n\mathrm{log}\left(n\right)$.

10Example

The example program reads a list of real numbers and ranks them into ascending order.

10.1Program Text

Program Text (m01dsce.c)

10.2Program Data

Program Data (m01dsce.d)

10.3Program Results

Program Results (m01dsce.r)