  Subconvexity bounds are proved for general Epstein zeta functions of k-ary
quadratic forms. This is related to sup-norm bounds for Eisenstein series on
GL(k), and the exact sup-norm exponent is determined to be (k-2)/8 for k >= 2.
In particular, if $k$ is odd, this exponent is not in Z/4, which shows that
Sarnak's purity conjecture does not hold for Eisenstein series.
