How can I solve this equation by using "fsolve" :

m
m
2012 12 25
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Functions = [a+b-c=0; -b+d+e=0; f+i-g=0; f+g=0; i-j=0; c=2; d=10; a=2g^2; b=f^3; i=e];

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Roger Stafford
Roger Stafford 2012-12-26
There is a very good reason why fsolve is having difficulties with your ten equations. If the obvious substitutions are made, they can be reduced to two cubic equations in the single unknown f:
f^3 + 2*f^2 - 2 = 0
f^3 + 2*f - 10 = 0
These two equations have no roots in common. Hence your ten equations can have no solution. They are mutally incompatible.
Roger Stafford

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回答（4 个）

m
m 2012-12-26
编辑：Andrei Bobrov 2012-12-26

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the output is:
>> fsolve(@(x) [x(1)+x(2)-x(3); -x(2)+x(4)+x(5); x(6)+x(8)-x(7); x(6)+x(7); x(8)-x(9); x(3)-2; x(4)-10; x(1)-2x(7)^2; x(2)-x(6)^3; x(8)-x(5)], ones(10,1))
??? fsolve(@(x) [x(1)+x(2)-x(3); -x(2)+x(4)+x(5); x(6)+x(8)-x(7); x(6)+x(7); x(8)-x(9); x(3)-2; x(4)-10; x(1)-2x(7)^2; x(2)-x(6)^3; x(8)-x(5)], ones(10,1))
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Error: Unexpected MATLAB expression.
Can you help me this is my homework and I have to give it tomorrow
m
m 2012-12-26
编辑：m 2012-12-26

0 个投票

there is a mistake: >> fsolve(@(x) [x(1)+x(2)-x(3); -x(2)+x(4)+x(5); x(6)+x(8)-x(7); x(6)+x(7); x(8)-x(9); x(3)-2; x(4)-10; x(1)-2*x(7)^2; x(2)-x(6)^3; x(8)-x(5)], ones(9,1))
Warning: Trust-region-dogleg algorithm of FSOLVE cannot handle non-square systems; using Levenberg-Marquardt algorithm instead. > In fsolve at 314
No solution found.
fsolve stopped because the last step was ineffective. However, the vector of function values is not near zero, as measured by the default value of the function tolerance.
criteria details
ans =
-0.3161
4.1390
2.9116
9.0718
-4.0046
1.6034
-0.5454
-3.0766
-3.0764
and also if we replace 9 with 10 the output:
>> fsolve(@(x) [x(1)+x(2)-x(3); -x(2)+x(4)+x(5); x(6)+x(8)-x(7); x(6)+x(7); x(8)-x(9); x(3)-2; x(4)-10; x(1)-2*x(7)^2; x(2)-x(6)^3; x(8)-x(5)], ones(10,1))
Solver stopped prematurely.
fsolve stopped because it exceeded the function evaluation limit, options.MaxFunEvals = 1000 (the default value).
ans =
-0.3362
4.1633
2.9138
9.0725
-3.9815
1.6063
-0.5392
-3.0588
-3.0536
1.0000
there is a mistake the numbers do not provide the equations

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m
m
2012-12-25

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