NETCDF(3f90) UNIDATA LIBRARY FUNCTIONS NETCDF(3f90)NAME
netcdf - Unidata Network Common Data Form (netCDF) library, version 3
interface
SYNOPSIS
use netcdf
Most Systems:
f90 ... -lnetcdf
CRAY PVP Systems:
f90 -dp -i64 ... -lnetcdf
LIBRARY VERSION
This document describes version 3 of Unidata netCDF data-access inter‐
face for the Fortran-90 programming language.
character*80 nf90_inq_libvers()
character(len=80) :: nf90_inq_libvers
Returns a string identifying the version of the netCDF library, and
when it was built, like: "3.1a of Aug 22 1996 12:57:47 $".
The RCS ident(1) command will find a string like "$Id: @(#) netcdf li‐
brary version 3.1a of Sep 6 1996 15:56:26 $" in the library. The SCCS
what(1) command will find a string like "netcdf library version 3.1a of
Aug 23 1996 16:07:40 $".
ROUTINE DESCRIPTIONS
All netCDF functions (except nf90_inq_libvers() and nf90_strerror())
return an integer status. This behavior replaces the rcode argument
used in previous versions of the library. If this returned status val‐
ue is not equal to nf90_noerr (zero), it indicates that an error oc‐
curred. The possible status values are defined in the module netcdf.
function nf90_strerror(ncerr)
integer, intent(in) :: ncerr
character(len=80) :: nf90_strerror
Returns a string textual translation of the ncerr value, like
"Attribute or variable name contains illegal characters" or "No
such file or directory".
function nf90_create(path, cmode, ncid)
character(len=*), intent(in) :: path
integer, intent(in) :: cmode
integer, optional, intent(in) :: initialsize
integer, optional, intent(inout) :: chunksize
integer, intent(out) :: ncid
integer :: nf90_create
(Corresponds to nccre() in version 2)
Creates a new netCDF dataset at path, returning a netCDF ID in
ncid. The argument cmode may include the bitwise-or of the fol‐
lowing flags: nf90_noclobber to protect existing datasets (de‐
fault silently blows them away), nf90_share for synchronous
dataset updates (default is to buffer accesses), and nf90_lock
(not yet implemented). When a netCDF dataset is created, is is
opened nf90_write. The new netCDF dataset is in define mode.
The optional argument initialsize sets the initial size of the
file at creation time.
See nf__open() below for an explanation of the optional chunk‐
size argument.
function nf90_open(path, mode, ncid, chunksize)
character(len=*), intent(in) :: path
integer, intent(in) :: mode
integer, intent(out) :: ncid
integer, optional, intent(inout) :: chunksize
integer :: nf90_open
(Corresponds to ncopn() in version 2)
Opens a existing netCDF dataset at path returning a netCDF ID in
ncid. As of NetCDF version 4.1, and if DAP support was enabled
when the library was built, the path may instead specify a DAP
URL (refer to the NetCDF user's manual for details).
The type of access is described by the mode parameter, which may
include the bitwise-or of the following flags: nf90_write for
read-write access (default read-only), nf90_share for synchro‐
nous dataset updates (default is to buffer accesses), and
nf90_lock (not yet implemented).
The optional argument referenced by chunksize controls a space
versus time tradeoff, memory allocated in the netcdf library
versus number of system calls. Because of internal require‐
ments, the value may not be set to exactly the value requested.
The actual value chosen is returned by reference. Using the
value nf90_sizehint_default causes the library to choose a de‐
fault. How the system choses the default depends on the system.
On many systems, the "preferred I/O block size" is available
from the stat() system call, struct stat member st_blksize. If
this is available it is used. Lacking that, twice the system pa‐
gesize is used. Lacking a call to discover the system pagesize,
we just set default chunksize to 8192.
The chunksize is a property of a given open netcdf descriptor
ncid: it is not a persistent property of the netcdf dataset.
function nf90_set_fill(ncid, fillmode, old_mode)
integer, intent(in) :: ncid, fillmode
integer, intent(out) :: old_mode
integer :: nf90_set_fill
Sets the fill-mode for a netCDF dataset to optimize writes under
some circumstances. The fill-mode argument, fillmode, can be
either nf90_fill or nf90_nofill. nf90_fill causes fill-values
to be written into non-record variables and into skipped-over
records when writing beyond the last valid record. nf90_nofill
suspends this behavior. The default behavior corresponds to
nf90_fill.
The previous fill-mode value is return in old_mode.
The fill-mode is a property of a given open netcdf descriptor
ncid: it is not a persistent property of the netcdf dataset.
function nf90_redef(ncid)
integer, intent(in) :: ncid
integer :: nf90_redef
(Corresponds to ncredf() in version 2)
Puts an open netCDF dataset into define mode, so dimensions,
variables, and attributes can be added or renamed and attributes
can be deleted.
function nf90_enddef(ncid, h_minfree, v_align, v_minfree, r_align)
integer, intent(in) :: ncid
integer, optional, intent(in) :: h_minfree, v_align
integer, optional, intent(in) :: v_minfree, r_align
integer :: nf90_enddef
(Corresponds to ncendf() in version 2)
Takes an open netCDF dataset out of define mode. The changes
made to the netCDF dataset while it was in define mode are
checked and committed to disk if no problems occurred. Some da‐
ta values may be written as well, see "VARIABLE PREFILLING" be‐
low. After a successful call, variable data can be read or
written to the dataset.
The optional arguments are performance tuning parameters. They
exposes internals of the netcdf version 1 file format and may
not be available on future netcdf implementations.
The current netcdf file format has three sections, the "header"
section, the data section for fixed size variables, and the data
section for variables which have an unlimited dimension (record
variables). The header begins at the beginning of the file. The
index (offset) of the beginning of the other two sections is
contained in the header. Typically, there is no space between
the sections. This causes copying overhead to accrue if one
wishes to change the size of the sections, as may happen when
changing names of things, text attribute values, adding at‐
tributes or adding variables. Also, for buffered i/o, there may
be advantages to aligning sections in certain ways.
The minfree parameters allow one to control costs of future
calls to nf90_redef(), nf90_enddef() by requesting that minfree
bytes be available at the end of the section. The h_minfree pa‐
rameter sets the pad at the end of the "header" section. The
v_minfree parameter sets the pad at the end of the data section
for fixed size variables.
The align parameters allow one to set the alignment of the be‐
ginning of the corresponding sections. The beginning of the sec‐
tion is rounded up to an index which is a multiple of the align
parameter. The flag value nf90_align_chunk tells the library to
use the chunksize (see above) as the align parameter. The
v_align parameter controls the alignment of the beginning of the
data section for fixed size variables. The r_align parameter
controls the alignment of the beginning of the data section for
variables which have an unlimited dimension (record variables).
The file format requires mod 4 alignment, so the align parame‐
ters are silently rounded up to multiples of 4. The usual call,
nf90_enddef(ncid) is equivalent to nf__enddef(ncid, 0, 4, 0, 4).
The file format does not contain a "record size" value, this is
calculated from the sizes of the record variables. This unfortu‐
nate fact prevents us from providing minfree and alignment con‐
trol of the "records" in a netcdf file. If you add a variable
which has an unlimited dimension, the third section will always
be copied with the new variable added.
function nf90_sync(ncid)
integer, intent(in) :: ncid
integer :: nf90_sync
(Corresponds to ncsnc() in version 2)
Unless the nf90_share bit is set in nf90_open() or nf90_cre‐
ate(), accesses to the underlying netCDF dataset are buffered by
the library. This function synchronizes the state of the under‐
lying dataset and the library. This is done automatically by
nf90_close() and nf90_enddef().
function nf90_abort(ncid)
integer, intent(in) :: ncid
integer :: nf90_abort
(Corresponds to ncabor() in version 2)
You don't need to call this function. This function is called
automatically by nf90_close() if the netCDF dataset was in de‐
fine mode and something goes wrong with the commit. If the
netCDF dataset isn't in define mode, then this function is
equivalent to nf90_close(). If it is called after nf90_redef(),
but before nf90_enddef(), the new definitions are not committed
and the dataset is closed. If it is called after nf90_create()
but before nf90_enddef(), the dataset disappears.
function nf90_close(ncid)
integer, intent(in) :: ncid
integer :: nf90_close
(Corresponds to ncclos() in version 2)
Closes an open netCDF dataset. If the dataset is in define
mode, nf90_enddef() will be called before closing. After a
dataset is closed, its ID may be reassigned to another dataset.
function nf90_inquire(ncid, ndims, nvars, natts, unlimdimid, nformat)
integer, intent(in) :: ncid
integer, optional, intent(out) :: ndims, nvars
integer, optional, intent(out) :: natts, unlimdimid
integer, optional, intent(out) :: nformat
integer :: nf90_inquire
Inquire about an open netCDF dataset. ncid is the netCDF ID of
the open dataset. Upon successful return, ndims will contain
the number of dimensions defined for this netCDF dataset, nvars
will contain the number of variables, natts will contain the
number of attributes, and unlimdimid will contain the dimension
ID of the unlimited dimension if one exists, or 0 otherwise.
nformat will contain the format version number, rarely needed
because the library detects the format version and behaves ap‐
propriately.
function nf90_def_dim(ncid, name, len, dimid)
integer, intent(in) :: ncid
character(len=*), intent(in) :: name
integer, intent(in) :: len
integer, intent(out) :: dimid
integer :: nf90_def_dim
(Corresponds to ncddef() in version 2)
Adds a new dimension to an open netCDF dataset, which must be in
define mode. name is the dimension name. len is the size of
the new dimension or nf90_unlimited to define the unlimited di‐
mension. On return, dimid will contain the dimension ID of the
newly created dimension.
function nf90_inq_dimid(ncid, name, dimid)
integer, intent(in) :: ncid
character(len=*), intent(in) :: name
integer, intent(out) :: dimid
integer :: nf90_inq_dimid
(Corresponds to ncdid() in version 2)
Given an open netCDF dataset and dimension name, returns the di‐
mension ID of the netCDF dimension in dimid.
function nf90_inquire_dimension(ncid, dimid, name, len)
integer, intent(in) :: ncid, dimid
character(len=*), optional, intent(out) :: name
integer, optional, intent(out) :: len
integer :: nf90_inquire_dimension
Inquire about a dimension. name should be big enough
(nf90_max_name) to hold the dimension name as the name will be
copied into your storage. The length return parameter, len will
contain the size of the dimension. For the unlimited dimension,
the returned length is the current maximum value used for writ‐
ing into any of the variables which use the dimension.
function nf90_rename_dim(ncid, dimid, name)
integer, intent(in) :: ncid
character(len=*), intent(in) :: name
integer, intent(in) :: dimid
integer :: nf90_rename_dim
(Corresponds to ncdren() in version 2)
Renames an existing dimension in an open netCDF dataset. If the
new name is longer than the old name, the netCDF dataset must be
in define mode. You cannot rename a dimension to have the same
name as another dimension.
function nf90_def_var(ncid, name, xtype, dimids, varid)
integer, intent(in) :: ncid
character(len=*), intent(in) :: name
integer, intent(in) :: xtype
integer, optional, dimension(:), intent(in) :: dimids
integer :: nf90_def_var
(Corresponds to ncvdef() in version 2)
Adds a new variable to a netCDF dataset. The netCDF must be in
define mode. name will be the name of the netCDF variable.
xtype is the external, netCDF type of the variable and should be
one of nf90_byte, nf90_char, nf90_short, nf90_int, nf90_float,
or nf90_double, The optional dimids argument contains the dimen‐
sion ID-s of the domain of the netCDF variable and, consequent‐
ly, determines the rank of the created variable: if dimids is
omitted, then the netCDF variable will be a scalar; if dimids is
a scalar, then the netCDF variable will be 1 dimensional; and if
dimids is a vector, then the netCDF variable will have rank
equal to the number of elements in dimids. varid will be set to
the netCDF variable ID.
function nf90_inq_varid(ncid, name, varid)
integer, intent(in) :: ncid
character(len=*), intent(in) :: name
integer, intent(out) :: varid
integer :: nf90_inq_varid
(Corresponds to ncvid() in version 2)
Returns the ID of a netCDF variable in varid given an open
netCDF dataset and the name of the variable.
function nf90_inquire_variable(ncid, varid, name, xtype, ndims, dimids,
natts)
integer, intent(in) :: ncid, varid
character(len=*), optional, intent(out) :: name
integer, optional, intent(out) :: xtype, ndims
integer, dimension(*), optional, intent(out) :: dimids
integer, optional, intent(out) :: natts
integer :: nf90_inquire_variable
Inquire about a netCDF variable in an open netCDF dataset, given
its variable ID. On return, name will contain the name of the
variable and should be capacious enough (nf90_max_name). xtype
will contain the external, netCDF type of the variable. ndims
will contain the dimensionality of the netCDF variable: if the
variable is a scalar, then size(ndims) will be zero; otherwise,
size(ndims) will be the rank of the variable and ndims will con‐
tain the dimension ID-s of the netCDF dimensions that constitute
the domain of the variable. natts will contain the number of
attributes associated with the netCDF variable.
function nf90_rename_var(ncid, varid, name)
integer, intent9in) :: ncid, varid
character(len=*), intent(in) :: newname
integer :: nf90_rename_var
(Corresponds to ncvren() in version 2)
Changes the name of a netCDF variable. If the new name is
longer than the old name, the netCDF must be in define mode.
You cannot rename a variable to have the name of any existing
variable.
function nf90_put_var(ncid, varid, values, start, stride, imap)
integer, intent(in) :: ncid, varid
<<whatever>>, intent(in) :: values
integer, dimension(:), optional, intent(in) :: start
integer, dimension(:), optional, intent(in) :: stride
integer, dimension(:), optional, intent(in) :: imap
integer :: nf90_put_var
(Replaces ncvpt() in version 2)
Writes a value or values to a netCDF variable. The netCDF
dataset must be open and in data mode. values contains the val‐
ue(s) what will be written to the netCDF variable identified by
ncid and varid; it may be a scalar or an array and must be of
type character, integer(kind=OneByteInt), inte‐
ger(kind=TwoByteInt), integer(kind=FourByteInt), inte‐
ger(kind=EightByteInt), real(kind=FourByteReal), or re‐
al(kind=EightByteReal). All values are converted to the exter‐
nal type of the netCDF variable, if possible; otherwise, an
nf90_erange error is returned. The optional argument start
specifies the starting index in the netCDF variable for writing
for each dimension of the netCDF variable. The optional argu‐
ment stride specifies the sampling stride (the interval between
accessed values in the netCDF variable) for each dimension of
the netCDF variable (see COMMON ARGUMENT DESCRIPTIONS below).
The optional argument imap specifies the in-memory arrangement
of the data values (see COMMON ARGUMENT DESCRIPTIONS below).
function nf90_get_var(ncid, varid, values, start, stride, imap)
integer, intent(in) :: ncid, varid
<<whatever>>, intent(out) :: values
integer, dimension(:), optional, intent(in) :: start
integer, dimension(:), optional, intent(in) :: stride
integer, dimension(:), optional, intent(in) :: imap
integer :: nf90_get_var
(Replaces ncvgt() in version 2)
Reads a value or values from a netCDF variable. The netCDF
dataset must be open and in data mode. values will receive the
value(s) what will be read from the netCDF
variable identified by ncid and varid; it may be a scalar or an
array and must be of type character, integer(kind=OneByteInt),
integer(kind=TwoByteInt), integer(kind=FourByteInt), inte‐
ger(kind=EightByteInt), real(kind=FourByteReal), or re‐
al(kind=EightByteReal). All values are converted from the ex‐
ternal type of the netCDF variable, if possible; otherwise, an
nf90_erange error is returned. The optional argument start
specifies the starting index in the netCDF variable for reading
for each dimension of the netCDF variable. The optional argu‐
ment stride specifies the sampling stride (the interval between
accessed values in the netCDF variable) for each dimension of
the netCDF variable (see COMMON ARGUMENT DESCRIPTIONS below).
The optional argument imap specifies the in-memory arrangement
of the data values (see COMMON ARGUMENT DESCRIPTIONS below).
function nf90_inquire_attribute(ncid, varid, name, xtype, len, attnum)
integer, intent(in) :: ncid, varid
character(len=*), intent(in) :: name
integer, optional, intent(out) :: xtype, len, attnum
integer :: nf90_inquire_attribute
Inquires about the netCDF attribute named name, of variable
varid, in the open netCDF dataset ncid. xtype will contain the
external, netCDF type of the variable. len will contain the
number of elements in the attribute. attnum will contain the
attribute number.
function nf90_inq_attname(ncid, varid, attnum, name)
integer, intent(in) :: ncid, varid, attnum
character(len=*), intent(out) :: name
integer :: nf90_inq_attname
(Corresponds to ncanam() in version 2)
Gets the name of an attribute, given its variable ID and at‐
tribute number. This function is useful in generic applications
that need to get the names of all the attributes associated with
a variable because attributes are accessed by name rather than
number in all other attribute functions (the number of an at‐
tribute is more volatile than the name because it can change
when other attributes of the same variable are deleted). The
attributes for each variable are numbered from 1 (the first at‐
tribute) to natts, where natts is the number of attributes for
the variable, as returned from a call to nf90_inquire_vari‐
able().
function nf90_put_att(ncid, varid, name, values)
integer, intent(in) :: ncid, varid
character(len=*), intent(in) :: name
<<whatever>>, intent(in) :: values
integer :: nf90_put_att
Unlike variables, attributes do not have separate functions for
defining and writing values. This function defines a new at‐
tribute with a value or changes the value of an existing at‐
tribute. If the attribute is new, or if the space required to
store the attribute value is greater than before, the netCDF
dataset must be in define mode. values contains the attribute
values to be written; it may be a scalar or a vector and must be
of type character, integer(kind=OneByteInt), inte‐
ger(kind=TwoByteInt), integer(kind=FourByteInt), inte‐
ger(kind=EightByteInt), real(kind=FourByteReal), or re‐
al(kind=EightByteReal).
function nf90_get_att(ncid, varid, name, fIvalues)
integer, intent(in) :: ncid, varid
character(len=*), intent(in) :: name
<<whatever>>, intent(out) :: values
integer :: nf90_get_att
(Replaces ncagt() in version 2)
Gets the value(s) of a netCDF attribute, given its variable ID
and name. The values are returned in values, which must be of
type character, integer(kind=OneByteInt), inte‐
ger(kind=TwoByteInt), integer(kind=FourByteInt), inte‐
ger(kind=EightByteInt), real(kind=FourByteReal), or re‐
al(kind=EightByteReal). Converts from the external type to the
type of the receiving variable, if possible; otherwise returns
an nf90_erange error. All values of the attribute are returned,
so you must allocate enough space to hold them. If you don't
know how much space to reserve, call nf90_inquire_attribute()
first to find out the length of the attribute.
function nf90_copy_att(ncid_in, varid_in, name, ncid_out, varid_out)
integer, intent(in) :: ncid_in, varid_in
character(len=*), intent(in) :: name
integer, intent(in) :: ncid_out, varid_out
integer :: nf90_copy_att
(Corresponds to ncacpy() in version 2)
Copies an attribute from one netCDF dataset to another. It can
also be used to copy an attribute from one variable to another
within the same netCDF dataset. ncid_in is the netCDF ID of an
input netCDF dataset from which the attribute will be copied.
varid_in is the ID of the variable in the input netCDF dataset
from which the attribute will be copied, or nf90_global for a
global attribute. name is the name of the attribute in the in‐
put netCDF dataset to be copied. ncid_out is the netCDF ID of
the output netCDF dataset to which the attribute will be copied.
It is permissible for the input and output netCDF ID's to be the
same. The output netCDF dataset should be in define mode if the
attribute to be copied does not already exist for the target
variable, or if it would cause an existing target attribute to
grow. varid_out is the ID of the variable in the output netCDF
dataset to which the attribute will be copied, or nf90_global to
copy to a global attribute.
function nf90_rename_att(ncid, varid, name, newname)
integer, intent(in) :: ncid, varid
character(len=*), intent(in) :: name, newname
integer :: nf90_rename_att
(Corresponds to ncaren()
Changes the name of an attribute. If the new name is longer
than the original name, the netCDF must be in define mode. You
cannot rename an attribute to have the same name as another at‐
tribute of the same variable. name is the original attribute
name. newname is the new name to be assigned to the specified
attribute. If the new name is longer than the old name, the
netCDF dataset must be in define mode.
function nf90_del_att(ncid, varid, name)
integer, intent(in) :: ncid, varid
character(len=*), intent(in) :: name
integer :: nf90_del_att
(Corresponds to ncadel() in version 2)
Deletes an attribute from a netCDF dataset. The dataset
must be in define mode.
COMMON ARGUMENT DESCRIPTIONS
In this section we define some common arguments which are used in the
"FUNCTION DESCRIPTIONS" section.
integer ncid
is the netCDF ID returned from a previous, successful call to
nf90_open() or nf90_create()
character(len=*) name
is the name of a dimension, variable, or attribute. It shall
begin with an alphabetic character, followed by zero or more al‐
phanumeric characters including the underscore (`_') or hyphen
(`-'). Case is significant. The maximum allowable number of
characters is nf90_max_name. Names that begin with an under‐
score (`_') are reserved for use by the netCDF interface.
integer xtype
specifies the external data type of a netCDF variable or at‐
tribute and is one of the following: nf90_byte, nf90_char,
nf90_short, nf90_int, nf90_float, or nf90_double. These are
used to specify 8-bit integers, characters, 16-bit integers,
32-bit integers, 32-bit IEEE floating point numbers, and 64-bit
IEEE floating-point numbers, respectively.
integer dimids
is a vector of dimension ID's and defines the shape of a netCDF
variable. The size of the vector shall be greater than or equal
to the rank (i.e. the number of dimensions) of the variable
(ndims). The vector shall be ordered by the speed with which a
dimension varies: dimids(1) shall be the dimension ID of the
most rapidly varying dimension and dimids(ndims) shall be the
dimension ID of the most slowly varying dimension. The maximum
possible number of dimensions for a variable is given by the
symbolic constant nf90_max_var_dims.
integer dimid
is the ID of a netCDF dimension. netCDF dimension ID's are al‐
located sequentially from the positive integers beginning with
1.
integer ndims
is either the total number of dimensions in a netCDF dataset or
the rank (i.e. the number of dimensions) of a netCDF variable.
The value shall not be negative or greater than the symbolic
constant nf90_max_var_dims.
integer varid
is the ID of a netCDF variable or (for the attribute-access
functions) the symbolic constant nf90_global, which is used to
reference global attributes. netCDF variable ID's are allocated
sequentially from the positive integers beginning with 1.
integer natts
is the number of global attributes in a netCDF dataset for the
nf90_inquire() function or the number of attributes associated
with a netCDF variable for the nf90_varinq() function.
integer start
specifies the starting point for accessing a netCDF variable's
data values in terms of the indicial coordinates of the corner
of the array section. The indices start at 1; thus, the first
data value of a variable is (1, 1, ..., 1). The size of the
vector shall be at least the rank of the associated netCDF vari‐
able and its elements shall correspond, in order, to the vari‐
able's dimensions.
integer stride
specifies the sampling interval along each dimension of the
netCDF variable. The elements of the stride vector correspond,
in order, to the netCDF variable's dimensions (stride(1)) gives
the sampling interval along the most rapidly varying dimension
of the netCDF variable). Sampling intervals are specified in
type-independent units of elements (a value of 1 selects consec‐
utive elements of the netCDF variable along the corresponding
dimension, a value of 2 selects every other element, etc.).
imap specifies the mapping between the dimensions of a netCDF vari‐
able and the in-memory structure of the internal data array.
The elements of the index mapping vector correspond, in order,
to the netCDF variable's dimensions (imap(1) gives the distance
between elements of the internal array corresponding to the most
rapidly varying dimension of the netCDF variable). Distances
between elements are specified in type-independent units of ele‐
ments (the distance between internal elements that occupy adja‐
cent memory locations is 1 and not the element's byte-length as
in netCDF 2).
VARIABLE PREFILLING
By default, the netCDF interface sets the values of all newly-defined
variables of finite length (i.e. those that do not have an unlimited,
dimension) to the type-dependent fill-value associated with each vari‐
able. This is done when nf90_enddef() is called. The fill-value for a
variable may be changed from the default value by defining the at‐
tribute `_FillValue' for the variable. This attribute must have the
same type as the variable and be of length one.
Variables with an unlimited dimension are also prefilled, but on an `as
needed' basis. For example, if the first write of such a variable is
to position 5, then positions 1 through 4 (and no others) would be set
to the fill-value at the same time.
This default prefilling of data values may be disabled by or'ing the
nf90_nofill flag into the mode parameter of nf90_open() or nf90_cre‐
ate(), or, by calling the function nf90_set_fill() with the argument
nf90_nofill. For variables that do not use the unlimited dimension,
this call must be made before nf90_enddef(). For variables that use
the unlimited dimension, this call may be made at any time.
One can obtain increased performance of the netCDF interface by using
this feature, but only at the expense of requiring the application to
set every single data value. The performance enhancing behavior of
this function is dependent on the particulars of the implementation and
dataset format. The flag value controlled by nf90_set_fill() is per
netCDF ID, not per variable or per write. Allowing this to change af‐
fects the degree to which a program can be effectively parallelized.
Given all of this, we state that the use of this feature may not be
available (or even needed) in future releases. Programmers are cau‐
tioned against heavy reliance upon this feature.
MPP FUNCTION DESCRIPTIONS
Additional functions for use on SGI/Cray MPP machines (_CRAYMPP).
These are used to set and inquire which PE is the base for MPP for a
particular netCDF. These are only relevant when using the SGI/Cray
``global'' Flexible File I/O layer and desire to have only a subset of
PEs to open the specific netCDF file. For technical reasons, these
functions are available on all platforms. On a platform other than
SGI/Cray MPP, it is as if only processor available were processor 0.
To use this feature, you need to specify a communicator group and call
glio_group_mpi() or glio_group_shmem() prior to the netCDF nf90_open()
and nf90_create() calls.
Note that the routines described below are Fortran-77 routines rather
than Fortran-90 routines (they have an "nf_" prefix rather than an
"nf90_" prefix).
integer function nf__create_mp(character*(*) path, integer cmode, inte‐
ger initialsize, integer pe, integer chunksize, integer ncid)
Like nf__create() but allows the base PE to be set.
The argument pe sets the base PE at creation time. In the MPP
environment, nf__create() and nf90_create() set the base PE to
processor zero by default.
integer function nf__open_mp(character*(*) path, integer mode, integer
pe, integer chunksize, integer ncid)
Like nf__open() but allows the base PE to be set. The argument
pe sets the base PE at creation time. In the MPP environment,
nf__open() and nf90_open() set the base PE to processor zero by
default.
integer function nf_inq_base_pe(integer ncid, integer pe)
Inquires of the netCDF dataset which PE is being used as the
base for MPP use. This is safe to use at any time.
integer function nf_set_base_pe(integer ncid, integer pe)
Resets the base PE for the netCDF dataset. Only perform this
operation when the affected communicator group synchronizes be‐
fore and after the call. This operation is very risky and
should only be contemplated under only the most extreme cases.
ENVIRONMENT VARIABLES
NETCDF_FFIOSPEC
Specifies the Flexible File I/O buffers for netCDF I/O when execut‐
ing under the UNICOS operating system (the variable is ignored on
other operating systems). An appropriate specification can greatly
increase the efficiency of netCDF I/O -- to the extent that it can
actually surpass FORTRAN binary I/O. This environment variable has
been made a little more generalized, such that other FFIO option
specifications can now be added. The default specification is bu‐
fa:336:2, unless a current FFIO specification is in operation,
which will be honored. See UNICOS Flexible File I/O for more in‐
formation.
MAILING-LISTS
Both a mailing list and a digest are available for discussion of the
netCDF interface and announcements about netCDF bugs, fixes, and en‐
hancements. To begin or change your subscription to either the mail‐
ing-list or the digest, send one of the following in the body (not the
subject line) of an email message to "majordomo@unidata.ucar.edu". Use
your email address in place of jdoe@host.inst.domain.
To subscribe to the netCDF mailing list:
subscribe netcdfgroup jdoe@host.inst.domain
To unsubscribe from the netCDF mailing list:
unsubscribe netcdfgroup jdoe@host.inst.domain
To subscribe to the netCDF digest:
subscribe netcdfdigest jdoe@host.inst.domain
To unsubscribe from the netCDF digest:
unsubscribe netcdfdigest jdoe@host.inst.domain
To retrieve the general introductory information for the mailing list:
info netcdfgroup
To get a synopsis of other majordomo commands:
help
SEE ALSOncdump(1), ncgen(1), netcdf(3f).
netCDF User's Guide, published by the Unidata Program Center, Universi‐
ty Corporation for Atmospheric Research, located in Boulder, Colorado.
Printed: 124.5.1 2000-04-04 NETCDF(3f90)
