NAG Library for SMP & Multicore, Mark 23

FSAI623DAL - License Managed

IBM AIX 64 (IBM POWER 7), IBM XL Fortran, Double Precision

Users' Note



Contents


1. Introduction

This document is essential reading for every user of the NAG Library for SMP & Multicore implementation specified in the title. It provides implementation-specific detail that augments the information provided in the NAG Mark 23 Library Manual (which we will refer to as the Library Manual). Wherever that manual refers to the "Users' Note for your implementation", you should consult this note.

In addition, NAG recommends that before calling any Library routine you should read the following reference material (see Section 5):

(a) Essential Introduction
(b) Chapter Introduction
(c) Routine Document

The libraries supplied with this implementation have been compiled in a manner that facilitates their use within a multithreaded application. If you intend to use the NAG library within a multithreaded application please refer to the document on Thread Safety in the Library Manual (see Section 5). Note that the system's default thread stacksize may not be sufficient for running all NAG Library for SMP & Multicore routines within multithreaded applications. You may have to increase this stacksize, e.g. using the POSIX threads routine pthread_attr_setstacksize. A value of 1MB should be sufficient in most circumstances, but more may be required if each POSIX thread is creating multiple OpenMP threads. You should consult a POSIX thread programming guide for further information if required.

2. Post Release Information

Please check the following URL:

http://www.nag.co.uk/doc/inun/fs23/ai6dal/postrelease.html

for details of any new information related to the applicability or usage of this implementation.

3. General Information

3.1. Accessing the Library

In this section we assume that the library has been installed in the directory [INSTALL_DIR].

By default [INSTALL_DIR] (see Installer's Note (in.html)) is /opt/NAG/fsai623dal or /usr/local/NAG/fsai623dal depending on your system; however it could have been changed by the person who did the installation. To identify [INSTALL_DIR] for this installation:

To use the NAG Library for SMP & Multicore and the IBM ESSL libraries, you may link in the following manner:
  xlf_r -q64 -qsmp=omp -qnosave -I[INSTALL_DIR]/nag_interface_blocks driver.f90 \
      [INSTALL_DIR]/lib/libnagsmp.a -lesslsmp 
where driver.f90 is your application program ; or
  xlf_r -q64 -qsmp=omp -qnosave -I[INSTALL_DIR]/nag_interface_blocks driver.f90 \
      [INSTALL_DIR]/lib/libnagsmp.so -lesslsmp
if the shareable library is required.

The library can be used with or without the compiler flag -qextname.

If your application has been linked with the shareable NAG library then the environment variable LD_LIBRARY_PATH must be set or extended, as follows, to allow run-time linkage.

In the C shell, type:

  setenv LD_LIBRARY_PATH [INSTALL_DIR]/lib
to set LD_LIBRARY_PATH, or
  setenv LD_LIBRARY_PATH [INSTALL_DIR]/lib:${LD_LIBRARY_PATH}
to extend LD_LIBRARY_PATH if you already have it set.

In the Bourne shell, type:

  LD_LIBRARY_PATH=[INSTALL_DIR]/lib
  export LD_LIBRARY_PATH
to set LD_LIBRARY_PATH, or
  LD_LIBRARY_PATH=[INSTALL_DIR]/lib:${LD_LIBRARY_PATH}
  export LD_LIBRARY_PATH
to extend LD_LIBRARY_PATH if you already have it set.

Note that you may also need to set LD_LIBRARY_PATH to point at other things such as compiler run-time libraries, for example if you are using a newer version of the compiler.

3.1.1. Setting the number of threads to use

Set the environment variable OMP_NUM_THREADS to the number of threads required, up to maximum available on your system.

In the C shell type:

  setenv OMP_NUM_THREADS N
In the Bourne shell, type:
  OMP_NUM_THREADS=N
  export OMP_NUM_THREADS
where N is the number of threads required. OMP_NUM_THREADS may be re-set between each execution of the program, as desired.

In general, the maximum number of threads you are recommended to use is the number of physical cores on your SMP system. However, IBM POWER7 processors support a facility known as SMT, which allows each physical core to support four threads at the same time and thus appear to the operating system four logical cores. It may be beneficial to make use of this functionality, but this choice will depend on the particular algorithms and problem size(s) used. You are advised to benchmark performance critical applications with and without SMT enabled, to determine the best choice for you. Enabling and disabling SMT may require root access to the system, although some sites may have configured different options in their batch queue systems to allow users to more easily access different SMT configurations.

3.2. Interface Blocks

The NAG Library for SMP & Multicore interface blocks define the type and arguments of each user callable NAG Library for SMP & Multicore routine. These are not essential to calling the NAG Library for SMP & Multicore from Fortran programs. However, they are required if the supplied examples are used. Their purpose is to allow the Fortran compiler to check that NAG Library for SMP & Multicore routines are called correctly. The interface blocks enable the compiler to check that:

(a) subroutines are called as such;
(b) functions are declared with the right type;
(c) the correct number of arguments are passed; and
(d) all arguments match in type and structure.

The NAG Library for SMP & Multicore interface block files are organised by Library chapter. They are aggregated into one module named

  nag_library
The modules are supplied in pre-compiled form (.mod files) and they can be accessed by specifying the -Ipathname option on each compiler invocation, where pathname ([INSTALL_DIR]/nag_interface_blocks) is the path of the directory containing the compiled interface blocks.

The .mod module files were compiled with the compiler shown in Section 2.1 of the Installer's Note. Such module files are compiler-dependent, so if you wish to use the NAG example programs, or use the interface blocks in your own programs, when using a compiler that is incompatible with these modules, you will first need to create your own module files. See the Post Release Information page

http://www.nag.co.uk/doc/inun/fs23/ai6dal/postrelease.html

where more information may be available, or contact NAG for further help.

3.3. Example Programs

The example results distributed were generated at Mark 23, using the software described in Section 2.2 of the Installer's Note. These example results may not be exactly reproducible if the example programs are run in a slightly different environment (for example, a different Fortran compiler, a different compiler library, or a different set of Basic Linear Algebra Subprograms (BLAS) or Linear Algebra PACKage (LAPACK) routines). The results which are most sensitive to such differences are: eigenvectors (which may differ by a scalar multiple, often -1, but sometimes complex); numbers of iterations and function evaluations; and residuals and other "small" quantities of the same order as the machine precision.

Note that the example material has been adapted, if necessary, from that published in the Library Manual, so that programs are suitable for execution with this implementation with no further changes. The distributed example programs should be used in preference to the versions in the Library Manual wherever possible. The directory [INSTALL_DIR]/scripts contains two scripts nagsmp_example and nagsmp_example_shar.

The example programs are most easily accessed by one of the commands

Each command will provide you with a copy of an example program (and its data and options file, if any), compile the program and link it with the appropriate libraries (showing you the compile command so that you can recompile your own version of the program). Finally, the executable program will be run with appropriate arguments specifying data, options and results files as needed.

The example program concerned, and the number of OpenMP threads to use, are specified by the arguments to the command, e.g.

nagsmp_example e04nrf 4
will copy the example program and its data and options files (e04nrfe.f90, e04nrfe.d and e04nrfe.opt) into the current directory, compile the program and run it using 4 OpenMP threads to produce the example program results in the file e04nrfe.r.

3.4. Fortran Types and Interpretation of Bold Italicised Terms

The NAG Library and documentation use parameterized types for floating-point variables. Thus, the type

      REAL(KIND=nag_wp)
appears in documentation of all NAG Library for SMP & Multicore routines, where nag_wp is a Fortran KIND parameter. The value of nag_wp will vary between implementations, and its value can be obtained by use of the nag_library module. We refer to the type nag_wp as the NAG Library "working precision" type, because most floating-point arguments and internal variables used in the library are of this type.

In addition, a small number of routines use the type

      REAL(KIND=nag_rp)
where nag_rp stands for "reduced precision type". Another type, not currently used in the library, is
      REAL(KIND=nag_hp)
for "higher precision type" or "additional precision type".

For correct use of these types, see almost any of the example programs distributed with the Library.

For this implementation, these types have the following meanings:

      REAL (kind=nag_rp)      means REAL (i.e. single precision)
      REAL (kind=nag_wp)      means DOUBLE PRECISION
      COMPLEX (kind=nag_rp)   means COMPLEX (i.e. single precision complex)
      COMPLEX (kind=nag_wp)   means double precision complex (e.g. COMPLEX*16)

In addition, the Manual has adopted a convention of using bold italics to distinguish some terms.

One important bold italicised term is machine precision, which denotes the relative precision to which DOUBLE PRECISION floating-point numbers are stored in the computer, e.g. in an implementation with approximately 16 decimal digits of precision, machine precision has a value of approximately 1.0D-16.

The precise value of machine precision is given by the routine X02AJF. Other routines in Chapter X02 return the values of other implementation-dependent constants, such as the overflow threshold, or the largest representable integer. Refer to the X02 Chapter Introduction for more details.

The bold italicised term block size is used only in Chapters F07 and F08. It denotes the block size used by block algorithms in these chapters. You only need to be aware of its value when it affects the amount of workspace to be supplied – see the parameters WORK and LWORK of the relevant routine documents and the Chapter Introduction.

3.5. Explicit Output from NAG Routines

Certain routines produce explicit error messages and advisory messages via output units which have default values that can be reset by using X04AAF for error messages and X04ABF for advisory messages. (The default values are given in Section 4.) These routines are potentially not thread safe and in general output is not recommended in a multithreaded environment.

4. Routine-specific Information

Any further information which applies to one or more routines in this implementation is listed below, chapter by chapter.
  1. C06

    In this implementation calls to the following FFT routines, from the ESSL library
     DCFT DCFT2 DCFT3 DCRFT DRCFT
    
    are made whenever possible in the following NAG routines:
     C06PAF  C06PCF  C06PFF  C06PJF  C06PKF  C06PQF  C06PRF  C06PSF
     C06PUF  C06PXF
    
    The required size of the workspace array WORK for each routine will depend upon the parameters used and thus the choice of ESSL or NAG FFT kernels used within the FFT routines. The values specified in the NAG routine documents should be sufficient in many cases, and where they are insufficient a suitable workspace will be allocated internally.
  2. F06, F07, F08 and F16

    In Chapters F06, F07, F08 and F16, alternate routine names are available for BLAS and LAPACK derived routines. For details of the alternate routine names please refer to the relevant Chapter Introduction. Note that applications should reference routines by their BLAS/LAPACK names, rather than their NAG-style names, for optimum performance.

    Many LAPACK routines have a "workspace query" mechanism which allows a caller to interrogate the routine to determine how much workspace to supply. Note that LAPACK routines from the ESSL library may require a different amount of workspace from the equivalent NAG versions of these routines. Care should be taken when using the workspace query mechanism.

    In this implementation calls to BLAS and LAPACK routines are implemented by calls to ESSL, except for the following routines:

    BLAS_DMAX_VAL    BLAS_DMIN_VAL
    DBDSDC    DBDSQR    DDISNA    DGBBRD    DGBCON    DGBEQU    DGBRFS    DGBSV
    DGBSVX    DGBTRF    DGBTRS    DGEBAK    DGEBAL    DGEBRD    DGEEQU    DGEES
    DGEESX    DGEEV     DGEEVX    DGEHRD    DGEJSV    DGELQF    DGELS     DGELSD
    DGELSS    DGELSY    DGEQLF    DGEQP3    DGEQPF    DGEQRF    DGERFS    DGERQF
    DGESDD    DGESV     DGESVD    DGESVJ    DGESVX    DGETRF    DGETRS    DGGBAK
    DGGBAL    DGGES     DGGESX    DGGEV     DGGEVX    DGGGLM    DGGHRD    DGGLSE
    DGGQRF    DGGRQF    DGGSVD    DGGSVP    DGTCON    DGTRFS    DGTSV     DGTSVX
    DGTTRF    DGTTRS    DHGEQZ    DHSEIN    DHSEQR    DLANGT    DLANSF    DLANST
    DNRM2     DOPGTR    DOPMTR    DORGBR    DORGHR    DORGLQ    DORGQL    DORGQR
    DORGRQ    DORGTR    DORMBR    DORMHR    DORMLQ    DORMQL    DORMQR    DORMRQ
    DORMRZ    DORMTR    DPBCON    DPBEQU    DPBRFS    DPBSTF    DPBSV     DPBSVX
    DPBTRF    DPBTRS    DPFTRF    DPFTRI    DPFTRS    DPOEQU    DPORFS    DPOSV
    DPOSVX    DPOTRS    DPPEQU    DPPRFS    DPPSV     DPPSVX    DPSTRF    DPTCON
    DPTEQR    DPTRFS    DPTSV     DPTSVX    DPTTRF    DPTTRS    DROTI     DROTM
    DROTMG    DSBEV     DSBEVD    DSBEVX    DSBGST    DSBGV     DSBGVD    DSBGVX
    DSBTRD    DSFRK     DSGESV    DSPCON    DSPEV     DSPEVD    DSPEVX    DSPGST
    DSPGV     DSPGVD    DSPGVX    DSPOSV    DSPRFS    DSPSV     DSPSVX    DSPTRD
    DSPTRF    DSPTRI    DSPTRS    DSTEBZ    DSTEDC    DSTEGR    DSTEIN    DSTEQR
    DSTERF    DSTEV     DSTEVD    DSTEVR    DSTEVX    DSYCON    DSYEV     DSYEVD
    DSYEVR    DSYEVX    DSYGST    DSYGV     DSYGVD    DSYGVX    DSYRFS    DSYSV
    DSYSVX    DSYTRD    DSYTRF    DSYTRI    DSYTRS    DTBCON    DTBRFS    DTBTRS
    DTFSM     DTFTRI    DTFTTP    DTFTTR    DTGEVC    DTGEXC    DTGSEN    DTGSJA
    DTGSNA    DTGSYL    DTPCON    DTPRFS    DTPTRS    DTPTTF    DTPTTR    DTRCON
    DTREVC    DTREXC    DTRRFS    DTRSEN    DTRSNA    DTRSYL    DTRTRS    DTRTTF
    DTRTTP    DTZRZF    ZBDSQR    ZCGESV    ZCPOSV    ZGBBRD    ZGBCON    ZGBEQU
    ZGBRFS    ZGBSV     ZGBSVX    ZGBTRF    ZGBTRS    ZGEBAK    ZGEBAL    ZGEBRD
    ZGEEQU    ZGEES     ZGEESX    ZGEEV     ZGEEVX    ZGEHRD    ZGELQF    ZGELS
    ZGELSD    ZGELSS    ZGELSY    ZGEQLF    ZGEQP3    ZGEQPF    ZGEQRF    ZGERFS
    ZGERQF    ZGESDD    ZGESV     ZGESVD    ZGESVX    ZGETRF    ZGETRS    ZGGBAK
    ZGGBAL    ZGGES     ZGGESX    ZGGEV     ZGGEVX    ZGGGLM    ZGGHRD    ZGGLSE
    ZGGQRF    ZGGRQF    ZGGSVD    ZGGSVP    ZGTCON    ZGTRFS    ZGTSV     ZGTSVX
    ZGTTRF    ZGTTRS    ZHBEV     ZHBEVD    ZHBEVX    ZHBGST    ZHBGV     ZHBGVD
    ZHBGVX    ZHBTRD    ZHECON    ZHEEV     ZHEEVD    ZHEEVR    ZHEEVX    ZHEGST
    ZHEGV     ZHEGVD    ZHEGVX    ZHERFS    ZHESV     ZHESVX    ZHETRD    ZHETRF
    ZHETRI    ZHETRS    ZHFRK     ZHGEQZ    ZHPCON    ZHPEV     ZHPEVD    ZHPEVX
    ZHPGST    ZHPGV     ZHPGVD    ZHPGVX    ZHPRFS    ZHPSV     ZHPSVX    ZHPTRD
    ZHPTRF    ZHPTRI    ZHPTRS    ZHSEIN    ZHSEQR    ZLANGT    ZLANHF    ZLANHT
    ZPBCON    ZPBEQU    ZPBRFS    ZPBSTF    ZPBSV     ZPBSVX    ZPBTRF    ZPBTRS
    ZPFTRF    ZPFTRI    ZPFTRS    ZPOEQU    ZPORFS    ZPOSV     ZPOSVX    ZPOTRS
    ZPPEQU    ZPPRFS    ZPPSV     ZPPSVX    ZPSTRF    ZPTCON    ZPTEQR    ZPTRFS
    ZPTSV     ZPTSVX    ZPTTRF    ZPTTRS    ZSPCON    ZSPMV     ZSPRFS    ZSPSV
    ZSPSVX    ZSPTRF    ZSPTRI    ZSPTRS    ZSTEDC    ZSTEGR    ZSTEIN    ZSTEQR
    ZSYCON    ZSYMV     ZSYRFS    ZSYSV     ZSYSVX    ZSYTRF    ZSYTRI    ZSYTRS
    ZTBCON    ZTBRFS    ZTBTRS    ZTFSM     ZTFTRI    ZTFTTP    ZTFTTR    ZTGEVC
    ZTGEXC    ZTGSEN    ZTGSJA    ZTGSNA    ZTGSYL    ZTPCON    ZTPRFS    ZTPTRS
    ZTPTTF    ZTPTTR    ZTRCON    ZTREVC    ZTREXC    ZTRRFS    ZTRSEN    ZTRSNA
    ZTRSYL    ZTRTRS    ZTRTTF    ZTRTTP    ZTZRZF    ZUNGBR    ZUNGHR    ZUNGLQ
    ZUNGQL    ZUNGQR    ZUNGRQ    ZUNGTR    ZUNMBR    ZUNMHR    ZUNMLQ    ZUNMQL
    ZUNMQR    ZUNMRQ    ZUNMRZ    ZUNMTR    ZUPGTR    ZUPMTR
    

    The following NAG named routines are wrappers to call LAPACK routines from the vendor library:
    F07FDF/DPOTRF    F07FRF/ZPOTRF    F07GDF/DPPTRF    F07GEF/DPPTRS
    F07GRF/ZPPTRF    F07GSF/ZPPTRS
    
  3. G02

    The value of ACC, the machine-dependent constant mentioned in several documents in the chapter, is 1.0D-13.
  4. P01

    On hard failure, P01ABF writes the error message to the error message unit specified by X04AAF and then stops.
  5. S07 - S21

    Functions in these Chapters will give error messages if called with illegal or unsafe arguments.

    The constants referred to in the Library Manual have the following values in this implementation:

    S07AAF  F_1 = 1.0E+13
            F_2 = 1.0E-14
    
    S10AAF  E_1 = 1.8715E+1
    S10ABF  E_1 = 7.080E+2
    S10ACF  E_1 = 7.080E+2
    
    S13AAF  x_hi = 7.083E+2
    S13ACF  x_hi = 1.0E+16
    S13ADF  x_hi = 1.8E+16
    
    S14AAF  IFAIL = 1 if X > 1.70E+2
            IFAIL = 2 if X < -1.70E+2
            IFAIL = 3 if abs(X) < 2.23E-308
    S14ABF  IFAIL = 2 if X > x_big = 2.55E+305
    
    S15ADF  x_hi = 2.65E+1
    S15AEF  x_hi = 2.65E+1
    S15AFF  underflow trap was necessary
    S15AGF  IFAIL = 1 if X >= 2.53E+307
            IFAIL = 2 if 4.74E+7 <= X < 2.53E+307
            IFAIL = 3 if X < -2.66E+1
    
    S17ACF  IFAIL = 1 if X > 1.0E+16
    S17ADF  IFAIL = 1 if X > 1.0E+16
            IFAIL = 3 if 0 < X <= 2.23E-308
    S17AEF  IFAIL = 1 if abs(X) > 1.0E+16
    S17AFF  IFAIL = 1 if abs(X) > 1.0E+16
    S17AGF  IFAIL = 1 if X > 1.038E+2
            IFAIL = 2 if X < -5.7E+10
    S17AHF  IFAIL = 1 if X > 1.041E+2
            IFAIL = 2 if X < -5.7E+10
    S17AJF  IFAIL = 1 if X > 1.041E+2
            IFAIL = 2 if X < -1.9E+9
    S17AKF  IFAIL = 1 if X > 1.041E+2
            IFAIL = 2 if X < -1.9E+9
    S17DCF  IFAIL = 2 if abs(Z) < 3.92223E-305
            IFAIL = 4 if abs(Z) or FNU+N-1 > 3.27679E+4
            IFAIL = 5 if abs(Z) or FNU+N-1 > 1.07374E+9
    S17DEF  IFAIL = 2 if Im(Z) > 7.00921E+2
            IFAIL = 3 if abs(Z) or FNU+N-1 > 3.27679E+4
            IFAIL = 4 if abs(Z) or FNU+N-1 > 1.07374E+9
    S17DGF  IFAIL = 3 if abs(Z) > 1.02399E+3
            IFAIL = 4 if abs(Z) > 1.04857E+6
    S17DHF  IFAIL = 3 if abs(Z) > 1.02399E+3
            IFAIL = 4 if abs(Z) > 1.04857E+6
    S17DLF  IFAIL = 2 if abs(Z) < 3.92223E-305
            IFAIL = 4 if abs(Z) or FNU+N-1 > 3.27679E+4
            IFAIL = 5 if abs(Z) or FNU+N-1 > 1.07374E+9
    
    S18ADF  IFAIL = 2 if 0 < X <= 2.23E-308
    S18AEF  IFAIL = 1 if abs(X) > 7.116E+2
    S18AFF  IFAIL = 1 if abs(X) > 7.116E+2
    S18DCF  IFAIL = 2 if abs(Z) < 3.92223E-305
            IFAIL = 4 if abs(Z) or FNU+N-1 > 3.27679E+4
            IFAIL = 5 if abs(Z) or FNU+N-1 > 1.07374E+9
    S18DEF  IFAIL = 2 if Re(Z) > 7.00921E+2
            IFAIL = 3 if abs(Z) or FNU+N-1 > 3.27679E+4
            IFAIL = 4 if abs(Z) or FNU+N-1 > 1.07374E+9
    
    S19AAF  IFAIL = 1 if abs(X) >= 5.04818E+1
    S19ABF  IFAIL = 1 if abs(X) >= 5.04818E+1
    S19ACF  IFAIL = 1 if X > 9.9726E+2
    S19ADF  IFAIL = 1 if X > 9.9726E+2
    
    S21BCF  IFAIL = 3 if an argument < 1.583E-205
            IFAIL = 4 if an argument >= 3.765E+202
    S21BDF  IFAIL = 3 if an argument < 2.813E-103
            IFAIL = 4 if an argument >= 1.407E+102
    
  6. X01

    The values of the mathematical constants are:

    X01AAF (pi) = 3.1415926535897932
    X01ABF (gamma) = 0.5772156649015328
    
  7. X02

    The values of the machine constants are:

    The basic parameters of the model

    X02BHF   = 2
    X02BJF   = 53
    X02BKF   = -1021
    X02BLF   = 1024
    X02DJF   = .TRUE.
    

    Derived parameters of the floating-point arithmetic

    X02AJF = 1.11022302462516E-16 X02AKF = 2.22507385850721E-308 X02ALF = 1.79769313486231E+308 X02AMF = 2.22507385850721E-308 X02ANF = 2.22507385850721E-308

    Parameters of other aspects of the computing environment

    X02AHF = 1.80143985094819E+16 X02BBF = 2147483647 X02BEF = 15 X02DAF = .TRUE.
  8. X04

    The default output units for error and advisory messages for those routines which can produce explicit output are both Fortran Unit 6.

5. Documentation

The Library Manual is available as part of the installation or via download from the NAG website. The most up-to-date version of the documentation is accessible via the NAG website at http://www.nag.co.uk/numeric/FL/FSdocumentation.asp.

The Library Manual is supplied in the following formats:

The following main index files have been provided for these formats:

	nagdoc_fl23/xhtml/FRONTMATTER/manconts.xml
	nagdoc_fl23/pdf/FRONTMATTER/manconts.pdf
	nagdoc_fl23/html/FRONTMATTER/manconts.html
Use your web browser to navigate from here. For convenience, a master index file containing links to the above files has been provided at
	nagdoc_fl23/index.html

Advice on viewing and navigating the formats available can be found in the Online Documentation document.

In addition the following are provided:

Please see the IBM web site for further information about ESSL (http://publib.boulder.ibm.com/infocenter/clresctr/vxrx/topic/com.ibm.cluster.essl.doc/esslbooks.html).

6. Support from NAG

(a) Contact with NAG

Queries concerning this document or the implementation generally should be directed to NAG at one of the addresses given in the Appendix. Users subscribing to the support service are encouraged to contact one of the NAG Response Centres (see below).

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Appendix - Contact Addresses

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