No you can't. If you delete the rows, the matrix will shrink. What you can do is to either set the nan elements to some known, constant value, or to fill in the nan regions with data from surrounding regions with something like regionfill() or a modified median filter. Would you like to do that? With regionfill() there is no max region size to fill in, but for a modified median filter you'd have to know the largest size of nan region in advance, which you can find.