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R: checking the sign of all terms in a long expression

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  • Subject: [mg132563] R: checking the sign of all terms in a long expression
  • From: "Brambilla Roberto Luigi (RSE)" <Roberto.Brambilla at rse-web.it>
  • Date: Sat, 12 Apr 2014 05:14:59 -0400 (EDT)
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ceck= a + a b - a b c + a c - b + b c - d

a - b + a b + a c + b c - a b c - d  (*NB rearranged order*)

pp = MonomialList[ceck] /. {a -> 1, b -> 1, c -> 1, d -> 1}

{-1, 1, 1, 1, 1, -1, -1}

Position[pp, -1]

 {{1}, {6}, {7}}

-----Messaggio originale-----
Da: dantimatter [mailto:google at dantimatter.com] 
Inviato: venerd=EC 11 aprile 2014 08:10
A: mathgroup at smc.vnet.net
Oggetto: checking the sign of all terms in a long expression


hello all
is there to check the signs of all terms in a symbolic expression, like

toCheck = a + a b + a b c + a c - b + bc + d ....

in this case, with the assumption that the a, b, c etc are all positive, only one term is negative (b by itself) and the rest are positive.  I have expressions like this that have a hundred or more terms and i'm worried i might not be catching all those that are of a different sign. 

thanks


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