Published online by Cambridge University Press: 20 November 2018
We prove a number of results about the stable and particularly the real ranks of tensor products of
${{C}^{*}}$
-algebras under the assumption that one of the factors is commutative. In particular, we prove the following:
(1) If $X$ is any locally compact
$\sigma $-compact Hausdorff space and
$A$ is any
${{C}^{*}}$-algebra, then
$\text{RR(}{{C}_{0}}\text{(}X\text{)}\otimes A\text{)}\le \text{dim(}X\text{)+RR(}A\text{)}$
.
(2) If $X$ is any locally compact Hausdorff space and
$A$ is any purely infinite simple
${{C}^{*}}$
-algebra, then
$\text{RR(}{{C}_{0}}\text{(}X\text{)}\otimes A\text{)}\le 1$
.
(3) $\text{RR(}C([0,\,1]\,)\otimes \,A)\,\ge \,1$ for any nonzero
${{C}^{*}}$-algebra
$A$, and
$\text{sr(}C({{[0,\,1]}^{2}})\,\otimes \,A\text{)}\,\ge \,2$ for any unital
${{C}^{*}}$-algebra
$A$.
(4) If $A$ is a unital
${{C}^{*}}$-algebra such that
$\text{RR(}A\text{)}\,\text{=}\,\text{0,}\,\text{s}r\text{(}A\text{)}\,\text{=}\,\text{1}$, and
${{K}_{1}}(A)=0$
, then
$\text{sr(}C([0,\,1])\,\otimes \,A\text{)}\,\text{=}\,1$.
(5) There is a simple separable unital nuclear
${{C}^{*}}$-algebra
$A$ such that
$\text{RR(}A\text{)}\,\text{=}\,\text{1}$ and
$\text{sr(}C([0,\,1])\,\otimes \,A\text{)}\,\text{=}\,1$.