Why I got complex answer while I know it should be real????
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Hi
I have a function to be solved. while I know it has a real answer I got complex answer, I check with 2 of my friends, one got real answer and the other one get the complex one as mine. what should I do? by the way,I want to solve it symbolic, This is the function and answer:
commands:
syms('x')
F=0.21*(exp(-0.157-0.157*x))-x
s=solve(F,x)
X=subs(s)
answer:
F = 21/(100*exp((157*x)/1000 + 157/1000)) - x
s =(1000*lambertw(0, -(100000*exp(157/1000))/3297))/157
X = 15.0552 +15.0159i
the answer tha my friend got with the same commands:
F =(21*exp(- (157*x)/1000 - 157/1000))/100 - x
s =(1000*lambertw(0, (3297*exp(-157/1000))/100000))/157
X = 0.1746
采纳的回答
owr
2013-1-29
0 个投票
My guess, and this may be a long shot, is that somewhere along the way you took the sqrt of -1.
更多回答（2 个）
Shashank Prasanna
2013-1-29
I got the same as your friend. Try the following
syms x F s X real
3 个评论
Shashank Prasanna
2013-1-29
编辑：Shashank Prasanna
2013-1-29
It seems to me that your F is different from your friends.
Fatemeh Eslami
2013-1-29
Fatemeh Eslami
2013-1-29
Walter Roberson
2013-1-29
0 个投票
Both F are the same, but your solve() is returning the wrong answer. The lambertw argument is of the form A*exp(-B) but your solve() is instead forming 1/A * exp(B) .
Which MATLAB versions are the two of you running? Is one of you running with the Maple based symbolic toolbox, and the other running with the MuPAD based symbolic toolbox?
Note: complex values are not inherently wrong solutions. The general solution is not restricted to LambertW branch 0 the way the two solutions here show.
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2013-1-29
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