Full Equations (FEQ) Model for the Solution of the Full, Dynamic Equations of Motion for One-Dimensional Unsteady Flow in Open Channels and Through Control Structures

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APPENDIX 3: Input-Output Unit Number Selection

As a consequence, a considerable history of input streams was developed for FEQ that required explicit unit numbers. These numbers continue to be supported in FEQ to maintain consistency with past use even though the use of unit numbers is no longer required in the current Fortran compilers and operating systems. As time permits and demand dictates, the old usage of unit numbers will be replaced with new usage that applies the more flexible facilities available on current operating systems. In the interim, the following guidelines for choosing unit numbers are offered.

1. Each operating system/language combination has a unique upper limit for unit numbers. In some cases, this is 99, but it may be larger or smaller than this value. The purpose of MUNIT in the INCLUDE file ARSIZE.PRM is to set this level so that the input can be checked in FEQ computations to make sure that the specified unit numbers are not too large for the operating system.
2. Fortran programming has defined standard unit numbers since the early beginnings, in the 1960's. Unit 5 was defined as a standard input, unit 6 as standard output to a line printer, and unit 7 was defined as output to a standard card punch. Card punches are not used anymore, and line printers are rarely used at this time. However, unit numbers 6 and 7 may have special significance for a given compiler of the Fortran programming language. Thus, these numbers should not be used for anything other than their original intent. Compilation and operation system difficulties may result if these unit numbers are applied in a nonstandard manner.
3. Command-line arguments are used in FEQ. A command line is the line following the DOS prompt on a DOS machine and the UNIX prompt on a UNIX machine. This is the line where words and strings of symbols are typed to tell the computer what actions should be done (the line where commands are issued to the computer). The first item included on a command line is the command. Items that follow the command, usually separated from the command and from each other by one or more spaces, are called command-line arguments. Two arguments are required with each a file name in FEQ simulation. The first argument is the name of the file that contains the input to FEQ as defined in the Input Description for the Full Equations model (section 13). This is the standard input file. The second argument is the name of the file that contains the items that are computed in the course of a simulation. This is the standard output file. An example command line for FEQ is FEQ FEQ.IN FEQ.OUT, where FEQ.IN is the name of the standard input file and FEQ.OUT is the name of the standard output file. The names for the standard input and output file are selected by the user and can be any valid name available in the operating system. As many as 64 characters may be used for the specification of the file name in FEQ. Therefore, a path can be included with the name.
4. Two standard unit numbers that relate the standard input and standard output files for FEQ are defined in a file STDUN.PRM, which may be retrieved electronically as described in section 1.1. These are the unit numbers that are equivalent in concept to unit numbers 5 and 6 in traditional Fortran. The Fortran parameter STD5 defines the unit number to use for processing the standard input file. The Fortran parameter STD6 defines the number to use for processing the standard output file. These parameters are 5 and 6, respectively, by default for DOS systems, but they need not have those values. Any valid values that the user selects may be used. Once selected, however, the unit numbers cannot be used for another purpose in the input to FEQ.
5. The Fortran-defined unit designation for writing to the display screen is used in FEQ. The unit field in an output statement in Fortran is given as an asterisk to denote output to the display screen. This means that an output to the standard output unit, STD6, will appear in the standard output file, whereas an output to a unit designated by an asterisk is to the display screen. This is the result on DOS systems. Some UNIX systems, however, define the asterisk unit differently. On these UNIX systems, the asterisk unit is associated with the standard output unit, 6. If this also is the unit used for the standard output file, then no text is written to the display screen and all text appears in the standard output file. Thus, to write to the display screen when running under UNIX, STD6 should not be given the number 6. Also, the standard unit number 5 is often associated with the keyboard in some UNIX systems. Therefore, STD5 and STD6 should not have the values of 5 and 6 under UNIX, but should be given some other numbers before the program is compiled. Values of 3 and 4 have been used in the past and have worked. On UNIX systems, unit numbers 5, 6, and 7 should be avoided because they may have a special meaning.
6. Aside from the standard unit numbers specified for STD5 and STD6 and the traditional standard unit numbers of 5, 6, and 7, the user may select the unit numbers. This choice is limited only by the following constraints:
   (A) the same unit number should not be used more than once in any context other than the input of files containing function tables, and
   (B) a unit number larger than the maximum value set by parameter MUNIT in INCLUDE file ARSIZE.PRM at the time the program was compiled should not be used.
   The units that have been referenced in FEQ simulation are monitored, and any duplicate reference results in an error.
7. The reuse of a unit number when processing files that contain function tables is allowed because these files are all processed in sequence and are processed completely before any other files referenced in the standard input to FEQ are processed. Use of a standard unit number for this purpose is recommended; unit number 15 is commonly applied for the unit number for processing each file containing function tables.
8. Standard numbers are recommended for files that appear in a common context. This would include the special-output file, the diffuse time-series file, and the files used to save and restore the state of the model. These numbers could all be less than some reasonable limit, such as 15. Then, numbers larger than 15 but no more than MUNIT are available for use in accessing point time-series files for input or output. The use of standard ranges will help avoid errors.