Re: Lists of Equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg106357] Re: [mg106307] Lists of Equations*From*: "David Park" <djmpark at comcast.net>*Date*: Sun, 10 Jan 2010 03:30:06 -0500 (EST)*References*: <1537969.1262943536382.JavaMail.root@n11>

Michael, I assume that zn[x] is an expression in x that you know independently? Then just define them first. z1[x_]:= ... z3[x_]:= ... etc. Then write your eqns statement. (eqs = {y1'[x]==z1[x], ..., yn'[x]==zn[x]})//Column where I have laid them out in a column - just for convenience. If there is a systematic pattern to the zn functions, you could write them as z[x_,k_]:= expression of x and k. or use SubValues: z[k_][x_]:= ... David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: Michael Knudsen [mailto:micknudsen at gmail.com] 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. Thanks, Michael Knudsen