The standard inverse scaling and squaring algorithm for computing the matri
x logarithm begins by transforming the matrix to Schur triangular form in o
rder to facilitate subsequent matrix square root and Pade approximation com
putations. A transformation-free form of this method that exploits incomple
te Denman-Beavers square root iterations and aims for a specified accuracy
(ignoring roundoff) is presented. The error introduced by using approximate
square roots is accounted for by a novel splitting lemma for logarithms of
matrix products. The number of square root stages and the degree of the fi
nal Pade approximation are chosen to minimize the computational work. This
new method is attractive for high-performance computation since it uses onl
y the basic building blocks of matrix multiplication, LU factorization and
matrix inversion.