README File for nec2c
- INTRODUCTION: nec2c is a translation of the NEC2 FORTRAN source code to the C language. The translation was performed mostly "by hand" and a lot of modifications to the original program were introduced in order to modernize the NEC2 and to remove as many built-in limitations as possible. The attendant SOMNEC program was also translated to C and incorporated in nec2c as a function so that Sommerfeld ground solutions are a part of the program.
- CHANGES:
The following is a list of the more significant changes incorporated into
nec2c during translation from FORTRAN to C:
- All GO TO constructs have been removed (all 961 of them!) and "spaghetti" code sections untangled as far as was possible to the author. Still, a lot of the code is not as clean and straightforward as might have been.
- Obsolete memory-saving practices (such as "equivalences" of different variables) have been eliminated and memory-sharing variables have been separated so that they are independent.
- All fixed-size arrays used in calculations have been replaced with buffer pointers which are allocated memory dynamically according to the needs of the program and the complexity of each structure's geometry. There is a two-fold advantage in this - there is virtually no limit to the complexity of a structure (number of segments/patches etc), and there is no wasted memory in fixed arrays. Additionally, there is no need for data storage/swapping between memory and files and therefore functions relating to this activity and also the NGF form of solution have been removed from the program.
- When a Sommerfeld finite ground solution is requested, since the SOMNEC program has been incorporated in nec2c there is no need to store the ground grid data in a file and read it when running nec2c. Instead, ground grid data are calculated as needed and for each new frequency if frequency stepping is specified.
- The factr() and solve() functions have been modified to handle the main matrix (cm) in untransposed form so that calculations are faster.
- The parser that reads the input file allows the two characters of the mnemonic to be in lower case if preferred. It also allows comments to be inserted anywhere in the input file in Unix style, e.g. all lines beginning with a '#' are ignored.
- Operationally, nec2c differs from NEC2 in not being an interactive application. Instead, nec2c is a non-interactive command-line application which accepts an input file name and optionally an output file name. If this is not specified, a name for the output file is made by stripping any extensions from the input file name and adding a ".out" extension. Furthermore, nec2c has the potential of being incorporated in another application (like a GUI) after suitable modifications, allowing the creation of a stand-alone program without the need for reading files produced separately.
- My original motive for translating NEC2 into C was to make it easier
to modify and modernize and to change obsolete functions and usage. As
a result I have edited to some extend the format of the output file to
make it more "human readable" (e.g. provided a single space between
adjacent numbers to avoid a hard-to-read "chain" of numbers joined by
- signs) etc. In my humble opinion these changes make the output file easier to read and possibly somewhat more presentable, although this is likely to be a problem with applications that read the output file in a rigid manner, based on the exact output format. I apologize for this change if it causes such problems but my intention is to eventually modify nec2c to be used as part of a graphical application, providing results for graphical plots directly in its buffers.
- COMPILATION:
The nec2c package is very simple at this time and compilation basically
only requires a Linux platform with development tools installed (gcc,
make and optionally gdb and Electric Fence for debugging). To compile the
source code just type "make nec2c" in the nec2c directory and if all is
well an executable binary (nec2c) should be produced. If gdb is not
installed, remove the -g option from the line in Makefile the reads:
CC = gcc -Wall -O3 -g
If the "Electric Fence" memory debugging tool is not installed, then
remove the -lefence option from the line in Makefile that reads:
$(CC) -lm -lefence -o nec2c $(objects) These changes can also be made if debugging is not of interest, thereby reducing the size of the binary and speeding it as well. If desired, nec2c can be properly installed by copying it to /usr/bin.
There is a double precision FORTRAN source (nec2dx.f) in this package and this can be compiled by typing "make nec2dx" in the nec2c directory. It can be run by typing ./nec2dx and supplying an input and output file name and it may be used to check nec2c's results for bugs etc.
4. USAGE: nec2c is run as a non-interactive command-line application and is invoked in the following manner: nec2c -i<input-file-name> [-o<output-file-name>][-hv]
-h: print this usage information and exit.
-v: print nec2c version number and exit.
The -i option is always needed and it specifies the name of the input file. The -o switch is optional and it specifies the output file name. If not used, a name for the output file is made by stripping any extensions from the input file name and adding a ".out" extension, e.g. nec2c -i yagi.nec will cause nec2c to read yagi.nec as the input file and produce yagi.out as the output file.
5. BUGS!!
Translating such a complex and large program from FORTRAN to C and making
so many changes along the way is very prone to bugs in the new program.
I have fixed a lot of these by using various input files that hopefully
invoke most if not all of NEC2's functions but there must still be bugs
in nec2c that will surface with some specific combinations of "cards" in
some input file. The best way to check nec2c's results is to run nec2dx
with the same input file and compare results - there should be very close
agreement between them as nec2dx is also double-precision.
6. Bug Fixes:
T.M. Sommers reported that input cards were being printed on a single
line. This was due to a '\n' (new line) that I presumably dropped when
I was editing the printout formats.
6. AUTHOR:
Neoklis Kyriazis neoklisk@cytanet.com.cy
January 27 2004