norm: Compute the Norm of a Matrix

Description Usage Arguments Details Value Source References See Also Examples

Description

Computes a matrix norm of x using LAPACK. The norm can be the one ("O") norm, the infinity ("I") norm, the Frobenius ("F") norm, the maximum modulus ("M") among elements of a matrix, or the “spectral” or "2"-norm, as determined by the value of type.

Usage

 1 norm(x, type = c("O", "I", "F", "M", "2"))

Arguments

 x numeric matrix; note that packages such as Matrix define more norm() methods. type character string, specifying the type of matrix norm to be computed. A character indicating the type of norm desired. "O", "o" or "1"specifies the one norm, (maximum absolute column sum); "I" or "i"specifies the infinity norm (maximum absolute row sum); "F" or "f"specifies the Frobenius norm (the Euclidean norm of x treated as if it were a vector); "M" or "m"specifies the maximum modulus of all the elements in x; and "2"specifies the “spectral” or 2-norm, which is the largest singular value (svd) of x. The default is "O". Only the first character of type is used.

Details

The base method of norm() calls the Lapack function dlange.

Note that the 1-, Inf- and "M" norm is faster to calculate than the Frobenius one.

Unsuccessful results from the underlying LAPACK code will result in an error giving a positive error code: these can only be interpreted by detailed study of the FORTRAN code.

Value

The matrix norm, a non-negative number.

Source

Except for norm = "2", the LAPACK routine DLANGE.

LAPACK is from http://www.netlib.org/lapack.

References

Anderson, E., et al (1994). LAPACK User's Guide, 2nd edition, SIAM, Philadelphia.