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
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채택된 답변
owr
2013년 1월 29일
My guess, and this may be a long shot, is that somewhere along the way you took the sqrt of -1.
추가 답변 (2개)
Shashank Prasanna
2013년 1월 29일
I got the same as your friend. Try the following
syms x F s X real
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Walter Roberson
2013년 1월 29일
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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