distmv.Bound is not defined

[biaojiang]

Hi, the code doesn't work since it was written in 2017.
My running environment is in Linux:
go 1.19.3
gonum 0.12.0

The errors are:

mixent.go:95:40: undefined: distmv.Bound
mixent.go:124:10: l.CovarianceMatrix(nil) (no value) used as value
mixent.go:125:10: r.CovarianceMatrix(nil) (no value) used as value

It seems distmv.Bound is not defined in any version of gonum.
So can you fix this problem, tks.