Re: seruous solve bug? only when used with simplifying

*To*: mathgroup at smc.vnet.net*Subject*: [mg48687] Re: [mg48634] seruous solve bug? only when used with simplifying*From*: DrBob <drbob at bigfoot.com>*Date*: Thu, 10 Jun 2004 02:44:05 -0400 (EDT)*References*: <200406090816.EAA15571@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Things are not quite as bad as you seem to think. sys = {c1[t] == (c*(16*a^4 + 8*a^3*kd + 4*a^2*apb*kd + 2*a*apb^2*kd + apb^3*kd))/(apb^4*kd), c2[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*d), c3[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*kd)}; sys1 = sys /. {apb -> a + b}; sys2 = Simplify[sys /. {apb -> a + b}]; sys3 = FullSimplify[sys /. {apb -> a + b}]; Simplify[sys1 == sys2] Simplify[sys1 == sys3] Simplify[sys2 == sys3] True True True Bobby On Wed, 9 Jun 2004 04:16:50 -0400 (EDT), sean kim <sean_incali at yahoo.com> wrote: > hello group, > > i think i have a serious Solve[], Simplify[], FullSimplify[] bug... > > > Take a system of equations as below. (apb is actually (a+b). i defined > it as apb to keep Mathematica crunching away at it) > > sys = > {c1[t] == (c*(16*a^4 + 8*a^3*kd + 4*a^2*apb*kd + 2*a*apb^2*kd + > apb^3*kd))/(apb^4*kd), > c2[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*d), > c3[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*kd)} > > sys1 = sys /.{apb -> (a + b)} > sys2 = sys/.{apb -> (a + b)}//Simplify > sys3 = sys/.{apb -> (a + b)}//FullSimplify > > and then use > > TrueQ[sys1 == sys1] > TrueQ[sys1 == sys2] > TrueQ[sys1 == sys3] > TrueQ[sys2 == sys3] > > then it gives, > > Out[18]=True > Out[19]=False > Out[20]=False > Out[21]=False > > Simplify and FullSimplify changed the system so much that they are not > equal? > > Basically, unless I define the (a+b) as a single constant apb, the Mathematica > will do soemthing with it then it messes it up. I think... > > Why is this happening? and how do i prevent it from happening again > with other more obsucre systems? Above I got lucky in finding the > cause (a+b) > > thanks in advance for any and all comments. > > Sean > > -- DrBob at bigfoot.com www.eclecticdreams.net/index.html

**References**:**seruous solve bug? only when used with simplifying***From:*sean_incali@yahoo.com (sean kim)