Re: simultaneous equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg2269] Re: [mg2232] simultaneous equations*From*: Lou Talman <me at talmanl.mscd.edu>*Date*: Thu, 19 Oct 1995 01:34:22 -0400

There is a syntax error in the third equation of your system. You should have had "r7880 (q78 +q80]^2", and not "r7880[q78 +q80]^2". --Lou Talman Begin forwarded message: >From: heath andersen <ha20 at uow.edu.au> >To: mathgroup at smc.vnet.net > Subject: [mg2232] simultaneous equations i am having trouble solving this set of simultaneous equations. it is probably my maths that is letting me down here, or lack of Mma use, or both, but, i can not work it out and have not had much luck asking round. In case u wanted to know i am trying to work out the volumetric flow rates for a dust extraction system, using an electrical analogy, where 'p' is the pressure(Pa), 'r' the resistance to flow and 'q' is the volumetric flow rate. the numbers ar the node opoints of the system, for example, 'p78', is the pressure at node 78, and 'p7880' is the node where 'p78' and 'p80' come together abd so on... also, [q7880]^2 = [q78 + q80]^2 Here is exactly what i typed in and what Mma gave me back. ---------------------------------------------------------------------------- -------- p78 = p80 = p81 = 101300 101300 p788081 = 100100.6 100100.6 r78 = r80 = 220 220 r81 = 219.5 219.5 r7880 = 54.86 54.86 Solve[{ p78 - p7880 == q78^2 * r78, p80 - p7880 == q80^2 * r80, p7880 - p788081 == r7880[q78 +q80]^2, p81 - p788081 == q81^2 * r81}, {q78, q80, p7880, q81}] Solve::tdep: The equations appear to involve transcendental functions of the variables in an essentially non-algebraic way. 2 Solve[{101300 - p7880 == 220 q78 , 2 101300 - p7880 == 220 q80 , 2 -100101. + p7880 == 54.86[q78 + q80] , 2 1199.4 == 219.5 q81 }, {q78, q80, p7880, q81}] ---------------------------------------------------------------------------- ---------- thanks h.andersen university of wollongong nsw australia