       Solving nonlinear equations with mathematica

• To: mathgroup at smc.vnet.net
• Subject: [mg35272] Solving nonlinear equations with mathematica
• From: Sebastian Pokutta <sebastian at pokutta.de>
• Date: Fri, 5 Jul 2002 02:21:41 -0400 (EDT)
• Organization: University of Essen, Germany
• Sender: owner-wri-mathgroup at wolfram.com

```Hi together,

I try to solve a system of 9 nonlinear Equations of the following forms:

Sum[(1/Sqrt[( S[[i, 1]] - X_j)^2 + ( S[[i, 2]] - Y_j)^2])*S[[i, 3]], {i, 1,
3}] = Z_j
( 1 <= j <= 9 )

I tried this with "findroot" and 9 Points (X_j,Y_j,Z_j)  ( 1 <= j <= 9 )
searching the S[[i,k]] ( a 3 x 3 matrix ) in the following way:

X = {{127, 17, 5.0316}, {118, 54, 1.9392}, {5, 10, 1.60571}, {67, 54,

1.04543}, {7, 15, 1.19647}, {24, 11, 1.10665}, {17, 21, 1.85287}, {31,

18, 1.59878}, {35, 7, 1.10325}};

FindRoot[{(1/Sqrt[(s11 - X[[1, 1]])^2 +
(s12 - X[[1, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[1, 1]])^2 + (s22 -
X[[1, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[1, 1]])^2 + (s32 - X[[1,
2]])^2])*s33 -
X[[1, 3]] ==
0, (1/Sqrt[(s11 - X[[2, 1]])^2 +
(s12 - X[[2, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[2, 1]])^2 + (s22 -
X[[2, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[2, 1]])^2 + (s32 - X[[2,
2]])^2])*s33 -
X[[2, 3]] ==
0, (1/Sqrt[(s11 - X[[3, 1]])^2 +
(s12 - X[[3, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[3, 1]])^2 + (s22 -
X[[3, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[3, 1]])^2 + (s32 - X[[3,
2]])^2])*s33 -
X[[3, 3]] ==
0, (1/Sqrt[(s11 - X[[4, 1]])^2 +
(s12 - X[[4, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[4, 1]])^2 + (s22 -
X[[4, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[4, 1]])^2 + (s32 - X[[4,
2]])^2])*s33 -
X[[4, 3]] ==
0, (1/Sqrt[(s11 - X[[5, 1]])^2 +
(s12 - X[[5, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[5, 1]])^2 + (s22 -
X[[5, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[5, 1]])^2 + (s32 - X[[5,
2]])^2])*s33 -
X[[5, 3]] ==
0, (1/Sqrt[(s11 - X[[6, 1]])^2 +
(s12 - X[[6, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[6, 1]])^2 + (s22 -
X[[6, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[6, 1]])^2 + (s32 - X[[6,
2]])^2])*s33 -
X[[6, 3]] ==
0, (1/Sqrt[(s11 - X[[7, 1]])^2 +
(s12 - X[[7, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[7, 1]])^2 + (s22 -
X[[7, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[7, 1]])^2 + (s32 - X[[7,
2]])^2])*s33 -
X[[7, 3]] ==
0, (1/Sqrt[(s11 - X[[8, 1]])^2 +
(s12 - X[[8, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[8, 1]])^2 + (s22 -
X[[8, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[8, 1]])^2 + (s32 - X[[8,
2]])^2])*s33 -
X[[8, 3]] ==
0, (1/Sqrt[(s11 - X[[9, 1]])^2 +
(s12 - X[[9, 2]])^2])*
s13 + (1/Sqrt[(s21 - X[[9, 1]])^2 + (s22 -
X[[9, 2]])^2])*
s23 + (1/Sqrt[(s31 - X[[9, 1]])^2 + (s32 - X[[9,
2]])^2])*s33 -
X[[9, 3]] == 0}, {s11, 130}, {s12, 54}, {s13, 11},
{s21, 125}, {s22,
10}, {s23, 34}, {s31, 5}, {s32, 33}, {s33, 8},
DampingFactor -> 2,
AccuracyGoal -> 4, MaxIterations -> 15
]

but "findroot" exits with:

FindRoot::"cvnwt": "Newton's method failed to converge to the prescribed
\
accuracy after \!\(15\) iterations."

But THERE'S a solution because I constructed the 9 Points using a given S
and just disturbed them with a random-value between 0 and 1. So is there a
sensible way to calculate the S sucht that the the error is minimal?

perhaps the way I constructed them:

given arbitrary X and Y the following equation calculates the Z.

ll[a_, b_] =
Sum[(1/Sqrt[( S[[i, 1]] - a)^2 + ( S[[i, 2]] -
b)^2])*S[[i, 3]], {i, 1,
3}] + Random[];

with the following S

S = {{130, 54, 11}, {125, 10, 34}, {5, 33, 8}};

Help would be greatly appreciated.

Cu,
Sebastian

--

Sebastian Pokutta

e-mail: sebastian at pokutta.de      oder    sebastian.pokutta at uni-essen.de
icq: 91203033

[sometimes simple means less than a week work :D] [don't drink and derive]

```

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