NAG Library Routine Document
M01EAF rearranges a vector of real numbers into the order specified by a vector of ranks.
||M1, M2, IRANK(M2), IFAIL
M01EAF is designed to be used typically in conjunction with the M01D ranking routines. After one of the M01D routines has been called to determine a vector of ranks, M01EAF can be called to rearrange a vector of real numbers into the rank order. If the vector of ranks has been generated in some other way, then M01ZBF
should be called to check its validity before M01EAF is called.
- 1: RV(M2) – REAL (KIND=nag_wp) arrayInput/Output
: elements M1
must contain real values to be rearranged.
On exit: these values are rearranged into rank order. For example, if , then the initial value of is moved to .
- 2: M1 – INTEGERInput
- 3: M2 – INTEGERInput
must specify the range of the ranks supplied in IRANK
and the elements of RV
to be rearranged.
- 4: IRANK(M2) – INTEGER arrayInput/Output
: elements M1
must contain a permutation of the integers M1
, which are interpreted as a vector of ranks.
On exit: used as internal workspace prior to being restored and hence is unchanged.
- 5: IFAIL – INTEGERInput/Output
must be set to
. If you are unfamiliar with this parameter you should refer to Section 3.3
in the Essential Introduction for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value
is recommended. If the output of error messages is undesirable, then the value
is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is
. When the value is used it is essential to test the value of IFAIL on exit.
unless the routine detects an error or a warning has been flagged (see Section 6
6 Error Indicators and Warnings
If on entry
, explanatory error messages are output on the current error message unit (as defined by X04AAF
Errors or warnings detected by the routine:
contain a value outside the range M1
contain a repeated value.
, elements M1
do not contain a permutation of the integers M1
. On exit, the contents of RV
may be corrupted. To check the validity of IRANK
without the risk of corrupting RV
, use M01ZBF
The average time taken by the routine is approximately proportional to , where .
This example reads a matrix of real numbers and rearranges its rows so that the elements of the
th column are in ascending order. To do this, the program first calls M01DAF
to rank the elements of the
th column, and then calls M01EAF to rearrange each column into the order specified by the ranks. The value of
is read from the datafile.
9.1 Program Text
Program Text (m01eafe.f90)
9.2 Program Data
Program Data (m01eafe.d)
9.3 Program Results
Program Results (m01eafe.r)