How can I save a Modis HDF-eos grid after analysis?

I'm reading a Modis level-3 product - for example:

http://e4ftl01.cr.usgs.gov//MODIS_Composites/MOTA/MCD43A4.005/2015.10.16/MCD43A4.A2015289.h12v04.005.2015310161057.hdf

Then, I'm reading it to matlab and perform some analysis - for example:

S = hdfinfo([pathname filename]);
NBAR_RED=hdfread(S.Vgroup.Vgroup(1).SDS(1)); 
NBAR_NIR=hdfread(S.Vgroup.Vgroup(1).SDS(2)); 
NBAR_RED=double(NBAR_RED);
NBAR_NIR=double(NBAR_NIR);
NDVI=(NBAR_NIR-NBAR_RED)./(NBAR_NIR+NBAR_RED);

How can I save NDVI as HDF-eos that is geographically matching the original image?