test ratio of DSYGV

[inn]

Test ratio | A Z - B Z D | / ( |A| |Z| n ulp ) is calculated for DSYGV with itype = 1 and uplo = 'U'.

In "dsg.out", it said that "For each pair (A,B), where A is of the given type
and B is a random well-conditioned matrix. D is diagonal, and Z is orthogonal."

In DSYGV, the input are A, B, lda, ldb, etc, without D and Z. And I couldn't find out the exact definition of Matrix D and Z. I just wonder how D and Z are calculated. Can anyone give me an explanation?