Re: "Reduce" wierdness (or too slow?)

• To: mathgroup at smc.vnet.net
• Subject: [mg16] Re: "Reduce" wierdness (or too slow?)
• From: TuesdayShopping <TuesdayShopping at yahoo.com>
• Date: Sun, 25 May 2008 02:02:18 -0400 (EDT)

```Re: Reduce" wierdness (or too slow?).
Thanks for the input from Andrzej Kozlowski, Daniel Lichtblau, Adam Strzebonski and others. OK; No inequations. Below is problem similar (not same) to the earlier one, that does not have any inequations but still Reduce will not solve it in 600 seconds. Even FindInstance will not find a (even partial) solution in 600 seconds. I should have got the solution for H, z2, w1, w2, t1, t2, t3, v2 as below. My goal is that I would like to solve a class of problems (like the one below) for as many variables as I can.

Problem:
Reduce[{1000 + t2 == t3, 1200 + w1 == w2, 125 + t1 == t2,
125 + t5 == t6, k*t3 == 2*(v2 + z2),
t7*z1 + t2*z2 + z3 + z4 == H + (t2^2)/k + (t7^2)/k + w1,
t7*z1 + t3*z2 + z3 + z4 == H + (t3^2 + t7^2)/k,
t7*z1 + z3 + z4 == 2*H + (t7^2)/k,
w1 + t6*z1 + z3 == (t6^2)/k + w1 + w2,
w1 == w2 + ((t1 - t2)*(t1 + t2 - k*z2))/k,
w2 + t5*z1 + z3 == (t5^2)/k + w1 + w2,
w2 == (-t1^2)/k + t1*z2 + z4, z1 == 2*t4/k + v2, z2 == 0}, {H, t1, t2, t3, t4, t5, t6, t7, v2, w1,
w2, z1, z2, z3, z4}, Reals, Backsubstitution -> True]

(For trying with FindInstance, add variable "k" to list of variables, and of course, remove "Backsubstitution -> True" option)

Solutions that must have been found:
t1 = ((48 * k - 625)/10),
t2 = ((48 * k + 625)/10),
t3 = ((48 * k + 10625)/10),
v2 = ((48 * k^2 + 10625 * k)/20),
w1 = ((9600 * k + 1125000)/k),
w2 = ((10800 * k + 1125000)/k),
z2 = 0,
H= z4 = ((2304 * k^2 + 1020000 * k + 112890625)/(100 * k))

```

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