Re: Coefficient with dot products
- To: mathgroup at smc.vnet.net
- Subject: [mg70579] Re: Coefficient with dot products
- From: Peter Pein <petsie at dordos.net>
- Date: Fri, 20 Oct 2006 05:21:44 -0400 (EDT)
- References: <eh4ocv$87e$1@smc.vnet.net>
Oliver Friedrich schrieb: > Hallo, > > I have some problems dealing with matrix equations: > > I have an equation > > m1.v1+m2.v2+m3.v3==0 > > where m are matrices and v are vectors. I want to use Coefficient on this > expression like > > Coefficient[%,v1] but this seems not to work if dot product instead of an > ordinary product is used. > How can I modify Coefficient or implement something on my own to fix this? > Hi Oliver, does In[1]:=Do[v[i] = {x[i], y[i]}; m[i] = {{m11[i], m12[i]}, {m21[i], m22[i]}}, {i, 3}] expr = Total[(m[#1] . v[#1] & ) /@ {1, 2, 3}] Out[2]= {m11[1]*x[1] + m11[2]*x[2] + m11[3]*x[3] + m12[1]*y[1] + m12[2]*y[2] + m12[3]*y[3], m21[1]*x[1] + m21[2]*x[2] + m21[3]*x[3] + m22[1]*y[1] + m22[2]*y[2] + m22[3]*y[3]} In[3]:= Transpose[(Coefficient[expr, #1] & ) /@ v[1]] Out[3]= {{m11[1], m12[1]}, {m21[1], m22[1]}} In[4]:= % == m[1] Out[4]= True solve your Problem? P²