negative data input to nmf (non-negative matrix factorization)

I want to apply non-negative matrix factorization on a data matrix of gene expression, but the matrix contain negative as well as positive data. the problem is Nmf does n't accept negative data. what should I do to make nmf work on this matrix??

[siva singireddi]

you must need to convert that matrix into positive.if you are analyzing the signals you will apply fft or stft technique to convert that matrix into positive these are the tools which convert the matrix, negative to positive.if you are analyzing the some elements please convert that negative elements into positive.