FSolve - no solution found, last step ineffective
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My function looks like this:
function F=Fn2(t)
global wn a g
F=(wn{1}^2)*a{1}(1,1)*sin(wn{1}*t)+(wn{2}^2)*a{2}(1,1)*sin(wn{2}*t)-g;
end
where wn, a, and g are defined in my main program. I call the function like this:
tlo=fsolve(@Fn2,1)
but fsolve can't seem to find a solution to the equation and is returning: "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."
"a" and "wn" are always real, and I've messed around with changing fsolve's x0 position. Any ideas why it's not working? Thanks in advance.
5 个评论
Perhaps there is no solution, for example, as would occur when
g > wn{1}^2*abs(a{1}(1,1)) + wn{2}^2*abs(a{2}(1,1))
Have you tested a case where the solution is known?
Incidentally, global variables are a discouraged method of passing fixed parameters to functions. You should really be doing this:
tlo=fsolve(@(t) Fn2(t,wn,a,g) ,1)
with Fn2 appropriately rewritten to accept (t,wn,a,g) as input arguments. See more info at http://www.mathworks.com/help/optim/ug/passing-extra-parameters.html
Eli
2013-11-28
Matt J
2013-11-28
What are the values of wn,a, and g and what is the corresponding solution t?
采纳的回答
Matt J
2013-11-28
FSOLVE can do it, but it has a rather narrow radius of capture around the desired tlo, roughly between 0.55 and .79
>> Fn2=@(t) (wn{1}^2)*a{1}(1,1)*sin(wn{1}*t)+(wn{2}^2)*a{2}(1,1)*sin(wn{2}*t)-g;
>> [tlo,fval] = fsolve(Fn2,.6,optimset('Display','none'))
tlo =
0.7667
fval =
7.1054e-15
3 个评论
Matt J
2013-11-28
There are also other solutions, of course,
>> [tlo,fval] = fsolve(Fn2,.51,optimset('Display','none'))
tlo =
1.2644
fval =
-3.5527e-14
Matt J
2013-11-28
FZERO has a fair bit larger radius of capture, roughly between .4 and 1.01
>> [tlo,fval] = fzero(Fn2,1)
tlo =
0.7667
fval =
7.1054e-15
Eli
2013-11-28
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