NAG Library Function Document

nag_rank_sort (m01dsc)

1  Purpose

2  Specification

3  Description

4  References

5  Arguments

1:     vec[$\mathbf{n}$] – const Pointer Input

On entry: the array of objects to be ranked.

2:     n – size_tInput

On entry: the number $n$ of objects.

Constraint: $\mathbf{n}\ge 0$.

3:     stride – ptrdiff_tInput

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. It should be noted that $\left|\mathbf{stride}\right|$ must be greater than or equal to size_of (data objects), for correct ranks to be produced. However, the code performs no check for violation of this constraint.

Constraint: $\left|\mathbf{stride}\right|>0$.

4:     compare – function, supplied by the userExternal Function

nag_rank_sort (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:     a – const Nag_Pointer Input

On entry: the first data field.

2:     b – const Nag_Pointer Input

On entry: the second data field.

5:     order – Nag_SortOrderInput

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:     ranks[n] – size_tOutput

On exit: the ranks of the corresponding data elements in vec.

7:     fail – NagError *Input/Output

The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

NE_BAD_PARAM

On entry, argument order had an illegal value.

NE_INT_ARG_EQ

On entry, $\mathbf{stride}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{stride}=0$.

NE_INT_ARG_GT

On entry, $\mathbf{n}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{n}\le ⟨\mathit{\text{value}}⟩$.

On entry, $\mathbf{stride}=⟨\mathit{\text{value}}⟩$.
Constraint: $\left|\mathbf{stride}\right|\le ⟨\mathit{\text{value}}⟩$.
These arguments are limited to an implementation-dependent size which is printed in the error message.

NE_INT_ARG_LT

On entry, $\mathbf{n}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{n}\ge 0$.

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example

10.1  Program Text

Program Text (m01dsce.c)

10.2  Program Data

Program Data (m01dsce.d)

10.3  Program Results

Program Results (m01dsce.r)