Matrix 1-norm, the maximum absolute column sum (LAPACK dlange with norm 1). This is the anorm rcond expects, computed before the matrix is factored.

A NaN entry carries through to the result, as dlange carries one through. Comparison alone would drop it, since every comparison against a NaN is false, and a norm that answers a finite number for a matrix it cannot describe would go on to be an anorm that hides what is in the matrix.

Frobenius norm (LAPACK dlange with norm F). Rescales like norm2 against overflow and underflow.

Matrix infinity-norm, the maximum absolute row sum (LAPACK dlange with norm I). A NaN carries through as it does in norm1.