I've done a bit of searching on Amazon and found the 1979 book by Philip J. Davis, but the typeset looks very old (blocked system print style) and I don't really like that. Does anyone know if there is a modern print version or a good alternative? Amazon doesn't really show much more else.
NB very loosely speaking circulant matrices are constructed from a single column vector, where each column of the matrix is a permutation of the previous column vector.
I eventually found an article by Ikra et al, 2012.