Three masses and four springs

*To*: mathgroup at smc.vnet.net*Subject*: [mg132597] Three masses and four springs*From*: Robert Jenkins <dale.jenkins8 at gmail.com>*Date*: Wed, 16 Apr 2014 03:40:27 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

The instruction DSolve[{-2*x1[t] + x2[t] == x1''[t], -2*x2[t] + x1[t] == x2''[t], x1[0] == -1, x2[0] == 2, x1'[0] == 0, x2'[0] == 0}, {x1, x2}, t] produces a simple solution. But I am surprised to find the three-mass version produces a mass of complication. Have I made a mistake? DSolve[{-2*x1[t] + x2[t] == x1''[t], -2*x2[t] + x3[t] + x1[t] == x2''[t], -2*x3[t] + x2[t] == x3''[t], x1[0] == -1, x2[0] == 2, x3[0] == -1, x1'[0] == 0, x2'[0] == 0, x3'[0] == 0}, {x1, x2, x3}, t]

**Follow-Ups**:**Re: Three masses and four springs***From:*Bob Hanlon <hanlonr357@gmail.com>