Re: Lists of Equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg106342] Re: Lists of Equations*From*: Albert Retey <awnl at gmx-topmail.de>*Date*: Fri, 8 Jan 2010 06:29:31 -0500 (EST)*References*: <hi6svt$9uu$1@smc.vnet.net>

Am 08.01.2010 10:13, schrieb Michael Knudsen: > Hello, > > I have just started using Mathematica, and I wonder what the easiest > way to manage a large set of equations is. I have a bunch of > differential equations > > y1'[x] = z1[x] > y2'[x] = z2[x] > .... > yn'[x] = zn[x] > > and I have grouped them together in a list like > > eqs = {y1'[x]==z1[x], ..., yn'[x]==zn[x]} > > which fits perfectly as an argument to NDSolve. However, I think that, > at a later point, I may have to use z1,...,zn separately, and I > thought about defining > > yeqs = {y1'[x],...,yn'[x]} > zeqs = {z1[x],...,zn[x]} > > and them combine them. What I would really like is something like > > yeqs + "==" + zeqs > > but I can't seem to find any list operation that will do that. Any > help is appreciated. I think Thread is your friend: Thread[yeqs==zeqs] you should also consider to take advantage of the possibility to use something as y[1] as a variable in NDSolve, which makes the handling of lists of expressions a lot easier: lhs = Table[y[i]'[x], {i, 1, 5}] rhs = Table[z[i][x], {i, 1, 5}] Thread[lhs == rhs] hth, albert