added some comments about dmnorm calculations
added some comments about dmnorm calculations

nxdao2000/nimble,nimble-dev/nimble,nxdao2000/nimble,nxdao2000/nimble,NLMichaud/nimble,nimble-dev/nimble,nimble-dev/nimble,NLMichaud/nimble,nimble-dev/nimble,nxdao2000/nimble,NLMichaud/nimble,nimble-dev/nimble,NLMichaud/nimble