Re: how to simplify an expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg90843] Re: how to simplify an expression*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sat, 26 Jul 2008 04:20:27 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <g6c971$bqv$1@smc.vnet.net>

mssivava wrote: > The following code calculates the elements of matrises (x6). But in the result there are some characters like #1,& vs. > And I couldn't success to express the result without these characters. Is there anyway to express more clear result? Please help!!!!!!!!! > > Thanks in advance > > > A = {{0, -R, 0, 0, 0, 0}, {(-Gamma^2*R^3*k)/Dnn, 0, -1,(R*(1 + Gamma^2))/Dnn, 0, 0}, {0, 1, 0, 0, (R*(1+ Gamma^2))/Dtt, (-R^2*Gamma^2)/Dtt}, {0, 0, 0, 0, -1, R}, {0, 0, 0, 1, 0, 0}, {k*R, 0, 0, 0, 0, 0}} > > expmat = MatrixExp[t*A] > expmat // MatrixForm > FullSimplify[expmat[[1, 1]]] The characters ("#!", "&", and the likes) you are referring to are parts of larger expressions called *Root[]*. Each Root[] object is an exact concise symbolic representation of a root. See http://reference.wolfram.com/mathematica/ref/Root.html If you want to get rid of them, you can use *ToRadicals[]*. See http://reference.wolfram.com/mathematica/ref/ToRadicals.html Note that, arguably, transforming Root[] objects into radicals might not be such a good idea since the complexity of the resulting matrix (measured in terms of binary tree size and depth) is dramatically increased. For instance, A = {{0, -R, 0, 0, 0, 0}, {(-Gamma^2*R^3*k)/Dnn, 0, -1, (R*(1 + Gamma^2))/Dnn, 0, 0}, {0, 1, 0, 0, (R*(1 + Gamma^2))/Dtt, (-R^2*Gamma^2)/Dtt}, {0, 0, 0, 0, -1, R}, {0, 0, 0, 1, 0, 0}, {k*R, 0, 0, 0, 0, 0}}; expmat = MatrixExp[t*A]; LeafCount[expmat[[1, 1]]] (* 7972 *) LeafCount[ToRadicals[expmat[[1, 1]]]] (* 74516 *) LeafCount[expmat] (* 232132 *) LeafCount[ToRadicals[expmat]] (* 2063994 *) Regards, -- Jean-Marc