Solve nonlinear equations within range
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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
采纳的回答
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)
8 个评论
Stephen
2018-10-17
madhan ravi
2018-10-17
编辑：madhan ravi
2018-10-17
Are you sure solx and soly return empty values
Matt J
2018-10-17
Empty values are the correct answer here. The equations have no solution for -1<=x<=+1.
madhan ravi
2018-10-17
+1 Oh thank you @Matt learnt a new method using vpasolve()
You can't apply bounds with fsolve, but you can with lsqnonlin. Yes, the input is to be a function handle. The function can reside anywhere that a function handle can find it, e.g., it can be a separate mfile, or a nested function, or an anonymous function, or a local function, or a class method, or a class-related function.
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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