R: Inverse from LU factorization

lu2inv {fastmatrix} | R Documentation

## Inverse from LU factorization

### Description

Invert a square matrix from its LU factorization.

### Usage

    lu2inv(x)

### Arguments

`x` | object representing an LU factorization. This will typically have come from a previous call to `lu`.

### Value

The inverse of the matrix whose LU factorization was given.

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.

### Source

This is an interface to the LAPACK routine `DGETRI`. LAPACK is from https://www.netlib.org/lapack/ and its guide is listed in the references.

### References

Anderson. E., Bai, Z., Bischof, C., Blackford, S., Demmel, J., Dongarra, J., Du Croz, J., Greenbaum, A., Hammarling, S., McKenney, A. Sorensen, D. (1999). LAPACK Users' Guide, 3rd Edition. SIAM. (Available at http://www.netlib.org/lapack/lug/lapack_lug.html).

Golub, G.H., Van Loan, C.F. (1996). Matrix Computations, 3rd Edition. John Hopkins University Press.

### See Also

`lu`, `solve`.

### Examples

    a <- matrix(c(3,2,6,17,4,18,10,-2,-12), ncol = 3)
    z <- lu(a)
    a %*% lu2inv(z)

[Package fastmatrix version 0.4 Index]