```Date: Mar 7, 2013 10:47 PM
Author: Sseziwa Mukasa
Subject: Re: Issue with the submatrix in mathematica(version 7)

Without knowing what the values of all the matrices you are using are, and what the intended outcome is I can't really help.  My guess is you expect Inverse[SPPS - TPSM.(Inverse[RMMinv]).TMPS] to be the inverse of (TPSP7 - TPSM.(Inverse[RMMinv]).RMP7).  I suspect that the condition number of  (TPSP7 - TPSM.(Inverse[RMMinv]).RMP7) is large.Regards,	SseziwaOn Mar 7, 2013, at 3:59 AM, Haosheng Shi <dvorak518@gmail.com> wrote:> I'm faced with a very strange problem in mathematica 7> In Algebra, if we decompose a matrix into some column vectors,such as> B={B1,B2...Bi...Bn}> then the product of the matrix is expected to be> A.B[[All,i]=(A.B)[[All,i]]>> mathematica gives a good result when dealing with symbols like A=Array[a,{n,n}]. But when cope with the numerical calculation, it will make some serious mistakes>> t1 = Inverse[SPPS - TPSM.(Inverse[RMMinv]).TMPS].(TPSPp - TPSM.(Inverse[RMMinv]).RMPp)[[1 ;; 12, 7]]> t2 = (Inverse[SPPS - TPSM.(Inverse[RMMinv]).TMPS].(TPSPp - TPSM.(Inverse[RMMinv]).RMPp))[[1 ;; 12, 7]]> t4 = Inverse[SPPS - TPSM.(Inverse[RMMinv]).TMPS].(TPSP7 - TPSM.(Inverse[RMMinv]).RMP7)>> the result is>> {2.28983*10^-16 + 2.22045*10^-16 I, -2.16493*10^-15 +>  2.10942*10^-15 I, 2.77556*10^-16 + 1.38778*10^-17 I,> 3.9443*10^-31 - 9.46633*10^-30 I, -1.10441*10^-29 ->  3.54987*10^-29 I, -8.67747*10^-30 - 2.36658*10^-29 I,> 1. - 2.498*10^-16 I, -2.22045*10^-16 ->  4.85723*10^-17 I, -1.31839*10^-16 + 1.66533*10^-16 I,> 3.15544*10^-30 + 3.47099*10^-29 I, -1.26218*10^-29 ->  2.52435*10^-29 I, 4.41762*10^-29 + 2.8399*10^-29 I}>> {2.42861*10^-16 + 3.46945*10^-16 I, -2.16493*10^-15 +>  2.10942*10^-15 I, 2.22045*10^-16 + 2.77556*10^-17 I,> 1.20178*10^-31 - 9.61886*10^-30 I, -1.32134*10^-29 ->  3.69902*10^-29 I, -9.26912*10^-30 - 2.41342*10^-29 I,> 1. - 2.498*10^-16 I, -2.63678*10^-16 ->  4.16334*10^-17 I, -1.249*10^-16 + 1.66533*10^-16 I,> 8.03652*10^-30 + 2.7339*10^-29 I, -1.76015*10^-29 - 2.55024*10^-29 I,>  4.22534*10^-29 + 2.86702*10^-29 I}>> {-0.0530074 - 0.0169643 I, -0.225895 - 0.0305394 I,> 0.0479921 - 0.0377367 I, -2.15746*10^-16 ->  6.66211*10^-16 I, -9.30951*10^-16 + 2.85235*10^-15 I,> 3.88901*10^-16 + 1.56189*10^-15 I,> 1.00746 + 0.0488354 I, -0.0227522 + 0.00304178 I,> 0.0678515 - 0.00137899 I,> 5.32924*10^-15 - 2.56555*10^-15 I, -2.99839*10^-15 +>  3.08487*10^-15 I, 3.60046*10^-16 - 4.89453*10^-15 I}>> Can you help me??>
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