> For the complete documentation index, see [llms.txt](https://docs.gasflow-mpi.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.gasflow-mpi.com/3.-brief-user-guide/3.3.-input-file-structure.md). # 3.3. Unit System and Files The system used in GASFLOW-MPI is the centimeter-gram-second (cgs) for the units of dimensional quantities. Therefore, the user should carefully use the following units when preparing input data:

Quantity	CGS unit name	Unit symbol	Unit definition	In SI units
length	centimeter	cm	1/100 of meter	10^−2 m
mass	gram	g	1/1000 of kilogram	10^-3 kg
time	second	s	1 second	1 s
temperature	kelvin	K	1 kelvin	1 K
force	dyne	dyn	g⋅cm/s^2	10^-5 N
pressure	barye	Ba	g/(cm⋅s^2)	10^-1 Pa
energy	erg	erg	g⋅cm^2/s^2	10^-7 J

If the cylindrical coordinate system is used to set up the mesh for computation, then input values for azimuthal coordinates, if required, must be in degrees (rather than in radiants). All the files used or written by GASFLOW-MPI are listed in the following table: ![](https://83179551-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FfznLyHTQno87OpY9VmJr%2Fuploads%2Fg882RYfEKl1e0kAMrXNW%2Fimage%20$25$.png?alt=media\&token=7d1b98b4-6790-4c30-951c-b094d205797a) To run GASFLOW-MPI, the user must prepare an input file that contains data required for the problem calculation and for specifying any desirable output options. The input file is called ingf. The user must limit the input file to 80 columns wide except for optional comments. The first three lines contain alphanumeric data for problem identification purposes. These input data follow: ![](https://83179551-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FfznLyHTQno87OpY9VmJr%2Fuploads%2FttCyHzBls17Toa1OONtg%2FImmagine%202022-06-22%20165144.png?alt=media\&token=46ae9637-7c1c-4af1-b4af-7f026e1241d5) The input data are read into the code via eight groups of NAMELIST variables. ![](https://83179551-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FfznLyHTQno87OpY9VmJr%2Fuploads%2FrzFa1kSaXZNehRSdMPoa%2FImmagine%202022-06-22%20165707.png?alt=media\&token=7ef393c9-efe1-42c6-8491-60fe051debf5) The NAMELIST feature offers an easy way of specifying input data. Within each NAMELIST group, both scalar and array variables can be defined conveniently with their desired values. An input NAMELIST group record can consist of one or more lines (physical records). Column 1 and column 81 and beyond are ignored. In the first line, $name (the dollar sign delimeter followed immediately by the name of NAMELIST group) must appear beginning in column 2 and then be followed by one or more blanks. The ramaining portion of the input record may contain as many variables as needed, with their assigned values, and in any order. Commas are used to separate items and to separate input values for elements of the same array. Input items take the following form: **Array** = value\[,value,]..., **array(subscripts)** = value\[,value,]..., Blanks can be used to improve legibility but must not be embedded in names, values, or between an array name and the open (left) parenthesis that encloses the array indices. For example, **gasdef(1:14,1)** = ...,is correct, whereas **gasdef (1:14,1)** = ..., will lead to input processing errors