Forms new matrices by adding up matrices from a file.

usage:

`summats `

`filename` `selection`` [`

`subtractionselection``]`

`filename` is the file containing the matrices to be
added. `selection` is a list (which can include ranges) of the
numbers of the matrices to be added in the file. 0 has a special
significance - it refers to a matrix whose off diagonal elements are
all 1 (and whose diagonal elements are chosen to make the rows sum to
0). 0 cannot be the only element in `selection` or
`subtractionselection`. `subtractionselection` is another
optional list of matrices, which are subtracted from the result of
adding the matrices in selection.

The resulting matrix is printed to standard output. It can be saved by redirecting standard output to a file. (Cutting and pasting is also possible, provided your screen is wide enough.)

Examples:

`summats matrices 0,3,5-9`

prints the sum of the matrices numbered 3,5,6,7,8,9 and the matrix all
of whose off-diagonal entries are 1, from the file `matrices`.

`summats matrices 1,2,4 9-36`

prints the sum of the matrices numbered 1,2 and 4 minus the sum of all
the matrices from 9 to 36 (inclusive) in the file `matrices`.

`summats matrices 0,5 5,1,3,8`

prints the result of subtracting the sum of matrices 1,3 and 8 from the matrix all of whose off-diagonal elements are 1.

[Bug: `summats` ignores the first matrix in the input
file. This is useful for parameter matrix files, where the line that
gives the number of matrices in the file is interpreted as a matrix.]