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Signs of coefficients in arrCharPoly http://www.singular.unikl.de/forum/viewtopic.php?f=10&t=2552 
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Author:  HyperFractal [ Sat Aug 20, 2016 12:21 pm ] 
Post subject:  Signs of coefficients in arrCharPoly 
Hello, this questions is about the function arrCharPoly in the arr.lib. I wonder what conventions there are concerning the signs of the entries of the output vector of arrCharPoly which computes the coefficients of the characteristic polynomial of an arrangements of hyperplanes. Sometimes the signs are correct but sometimes plus and minus are swapped. I thought this could be due to the dimension of the ambient space (because of some factor like (1)^n) but this seems not to be the case. Then I thought this could be due to the fact whether there is a constant term or not  but I am not sure about this. Many thanks for your help, HyperFractal 
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