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Solve nonlinear equations within range

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Stephen
Stephen 2018-10-17
编辑： Matt J 2018-10-19
Hello,
I have two nonlinear equations to solve simultaneously:
syms x, y
f1 = x^2 + y^2 + x == 4
f2 = x^3 + y*2 == 2
I want to find the solutions (if there's any), when x belongs to the range of [-1,1]. And I don't want to make another matlab file whose purpose is to group the above equations. Because most of the time, the equations are derived from the using symbolic tools earlier in same matlab script and it would be inconvenient to make a separate file.
In this case, what is the way to achieve my goal?
Thanks in advance.
Steph

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采纳的回答

Matt J
Matt J 2018-10-17
syms x y
assume(x>=-1 & x<=1)
f1 = x^2 + y^2 + x == 4
f2 = x^3 + y*2 == 2
[solx,soly]=vpasolve(f1,f2,x,y)
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Stephen
Stephen 2018-10-19
编辑：Stephen 2018-10-19
Isn't that function is supposed to be used for curve fitting?
How do I convert those two non-linear equations so that I can use lsqnonlin?
Matt J
Matt J 2018-10-19
编辑：Matt J 2018-10-19
Example:
fun=@(p) [p(1)^2+p(2)^2+p(1)-4; p(1)^2+2*p(2)-2];
[p,resnorm,~,exitflag]=lsqnonlin(fun,[0,0],[-3,-inf],[+3,+inf])
if resnorm>TOO_BIG
warning 'The result does not satisfy equations well.'
end

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