Re: Converting set of equations to matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg26728] Re: Converting set of equations to matrix*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 19 Jan 2001 02:14:06 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <9462b7$gc8@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, a) your equations will never yield the matrix you give b) In[]:=eqn = {3 a[0, 0] + 2 a[0, 2] + 4 a[2, 0] == 0, -1 a[0, 0] + 0.3 a[2, 0] == 0, 4 a[0, 2] - 1 a[2, 0] == 0} In[]:=Outer[D, First /@ eqn, {a[0, 0], a[0, 2], a[2, 0]}] gives the matrix. It may be useful for general equations to use Outer[D, First /@ (eqn /. q_==r_ :> q-r==0), {a[0, 0], a[0, 2], a[2, 0]}] Regards Jens Helge Kreutzmann wrote: > > Hello ! > I have a set of equations I create following some rules, like > > 3 a[0,0] + 2 a[0,2] + 4 a[2,0] = 0 > -1 a[0,0] + 0.3 a[2,0] = 0 > 4 a[0,2] - 1 a[0,2] = 0 > > The numbers of coefficients (the a[i,j]) is different in each run > but fixed. For further calculations I would like to transform the > above equations into the matrix > {{3,2,4 },{-1,0,0.3},{0,4,-1}} > > Currently I have a list (called coeffli) where I can get the equations > from. The existing coefficients are stored in a second list (klist). > I also have a list where the values i,j are stored (cplist). > > The above list I would create by > For[i = 1, i <= Length[kflist], i++, > Print[Collect[coeffli[[cplist[[i]][[1]]]][[cplist[[i]][[2]]]], klist]]] > > I can create a list of the equations but I do not know how to tear > apart the sum into matrix elements. > > Thanks > > Helge