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Re: Lists of Equations
*To*: mathgroup at smc.vnet.net
*Subject*: [mg106358] Re: [mg106307] Lists of Equations
*From*: Bob Hanlon <hanlonr at cox.net>
*Date*: Sun, 10 Jan 2010 03:30:18 -0500 (EST)
*Reply-to*: hanlonr at cox.net
It is generally more convenient to use the form z[1][x] rather than z1[x]
n = 3;
yVar = Array[y, n];
zVar = Array[z, n];
zx = Through[zVar[x]]
{z[1][x], z[2][x], z[3][x]}
which is equivalent to
zx = (#[x] & /@ zVar)
{z[1][x], z[2][x], z[3][x]}
dy = D[Through[yVar[x]], x]
{Derivative[1][y[1]][x], Derivative[1][y[2]][x], Derivative[1][y[3]][x]}
which is equivalent to
dy = (#'[x] & /@ yVar)
{Derivative[1][y[1]][x], Derivative[1][y[2]][x], Derivative[1][y[3]][x]}
eqs = Thread[dy == zx]
{Derivative[1][y[1]][x] == z[1][x], Derivative[1][y[2]][x] == z[2][x],
Derivative[1][y[3]][x] == z[3][x]}
Bob Hanlon
---- Michael Knudsen <micknudsen at gmail.com> wrote:
=============
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
--
Bob Hanlon
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