Depending on the requirements of a run, NEC-2 may use the following files.

- 11,12,13,14,15,16 - scratch files for matrix manipulations.
- 20 - NGF file
- 21 - Sommerfeld/Norton data.

The scratch files are used only when the matrix will not fit into core stroage. Fro a case that does not use the NGF (but may write a NGF file), there are five options for matrix storage. IF

- N=the number of equations (number of segments plus twice the number of patches),
- N
_{x}=the number of equations for a symmetric section, and - I
_{R}=number of complex numbers for the matrix in core storage (4000),

then the case, indicated by the value of ICASE in the code, are

- matrix in core, no symmetry (N
^{2}<=I_{R}). - matrix in core,symmetry (NN
_{x}<=I_{R}). - matrix in core, no symmetry (N
^{2}>=I_{R}). - matrix in core,symmetry blocks fit in core (NN
_{x}> I_{R},N_{x}^{2}<=I_{R}). - matrix out of core,symmetry blocks do not fit in core
N
_{x}^{2}>I_{R}).

File storage is used in cases 3,4 and 5. Only the four files (11,12,13 and
14) are used when the NGF is not in use. The size of
each file is approximately @NN_{x} words. If the computer system
requires that the user specify the file size, a safety margin should be
included in the request. A more accurate estimate of the file size is

- L=2NN
_{c}[N_{x}/N_{c}],

Where

- N
_{c}=[I_{R})/(2N)]

and [ ] indicates truncation. N_{c}, which is the number of matrix
columns in I/O block, must be at least 1.

When the NGF is used, all six scratch files may be
required. For the NGF the matrix is partitioned into
four sections as

_ _ |A B| |C D| - -

A is the matrix for the NGF structure and is factored before the NGFfile is written. The stroage case for A is indicated in the NGFlable by the value of ICASE (see exampel 10 in section IV). When the NGF is used, matrix A is read from file 20 and, if ICASE is 3,4, or 5, is stored on file 13. The size of file 13 when the NGF is used is approximately:

ICASELength of file 133 4N

^{2} 4 2NN_{x} 5 4NN_{x} There are four options for
storage of the matrices B, C, and D. these are associated with the integer
ICASX as follows:

__ICASE__

- A
_{R}, B, C, and D fit in core together where

A_{R}=A for ICASE=1 or 2,

=one I/O block of A for ICASE=3 or 5,

=one submatrix for ICASE=4 - B, C, an dD fit in core but not with A
_{R}. This is possible only for ICASE=3, 4, or 5 when A does not need dedicated space in core. A_{R}an dB must also fit in core together. - B, C, and D do not fit in core, but D fits in core alone.

A and D must fit together if ICASE=1 or 2. - D does not fit in core.

The sizees of matrices B, C, and D depend on the number of new unknowns
N_{n} where

- N
_{n}=N_{n}+N_{t}+2N_{p}+10N_{q} - N
_{s}=number of new segments added to NGF, - N
_{t}=number of NGF segments connected to new segments or patches, - N
_{p}=number of new patches, - N
_{q}=number of NGF patches connected to new segments.

The sizes of matrices B and C are 2NN_{n} and the size of D is
2N_{n}^{2} words. The file lengths are approximately
2N_{n}^{2} words for files 11 and 12 and 2NN_{n} for
files 14, 15 and 16. when ICASX is 1 these files are not used, and when ICASX
is 2 file 16 is not used.

The length of the NGF file (20) is approximately
4N(N_{x}+3). The length of the Summerfeld/Norton data file (21) is
about 2200 words.