```Date: Feb 15, 2013 9:50 AM
Author: Milos Milenkovic
Subject: Solve the system of equations II

Dear all, > > > > what if there is an implicit conditional equation like D=B*X*B' + A*X*A', X=?, A,B,D are known. Can I use the concept proposed by Greg? Best,M> > > > > > > > A=[0.06 0.07 0.08 0.09 0.1 0.09; 0.01 0.02 0.03 0.04 0.05 0.06; -0.01 -0.02 -0.03 -0.04 -0.04 0.05; 0 0.01 0.02 0.03 0.04 0.05; -0.06 -0.05 -0.04 -0.03 -0.02 -0.01; 0.01 0.02 0.03 0.04 0.05 0.06];   B=[-1 0 0 0 0 0; 0 -1 0 0 0 0; 0 0 -1 0 0 0; 0 0 0 -1 0 0; 0 0 0 0 -1 0; 0 0 0 0 0 -1]; > > > > D=[0.57 0.57 23.96 0 0.57 0.57; 0.57 0.57 23.96 0 0.57 0.57; 23.96 23.96 3027.70 0 23.96 23.96;0 0 0 0 0 0;0.57 0.57 23.96 0 0.57 0.57;0.57 0.57 23.96 0 0.57 0.57];Greg's approach =>> > > >> condA = cond(A)> > > condB = cond(B)> > > > > > condA = 1.4662e+017> > > condB = 1> > > > > > >> X = pinv(A)*D/B> > > > > > X = 1.0e+005 *> > > > > > -0.0127 -0.0127 -1.5421 0 -0.0127 -0.0127> > > 0.0001 0.0001 0.0026 0 0.0001 0.0001> > > 0.0128 0.0128 1.5472 0 0.0128 0.0128> > > 0.0255 0.0255 3.0919 0 0.0255 0.0255> > > -0.0258 -0.0258 -3.1043 0 -0.0258 -0.0258> > > 0.0001 0.0001 0.0055 0 0.0001 0.0001> > > > > > >> E = norm(D-A*X*B)> > > > > > E = 20.3620> > > > >> F = norm(D)> > > > F = 3.0285e+003> > > > >> G = norm(A*X*B)> > > > G = 3.0284e+003> > > > >> relerr = E/F> > > > relerr = 0.0067
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