Why does my objective function return complex?

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Snoopy 2022-2-28

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评论： Walter Roberson 2022-3-2

I have a likelihood function that I need to minimize. I use fmincon to search for the minimum. Iterations of fmincon sometimes show "Objective function returned complex; trying a new point…" But in my code I do not take square root of any variable. Why am I then getting this error? A second question is whether there is a counterpart of

dbstop if naninf

for "complex" like the

dbstop if complex

command? Or would

dbstop if error

do?

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Torsten 2022-2-28

log(x), x^a and sqrt(x) are the most common sources to get complex numbers.

David Goodmanson 2022-2-28

also asin and acos

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采纳的回答

Matt J 2022-2-28

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编辑：Matt J 2022-2-28

在 MATLAB Online 中打开

There is no "dbstop if complex", but you can set a conditional breakpoints in your objective function to detect when theany particular value is complex.Or, insert a keyboard() command.

function fval=myobjective(x)
fval=....
    
    if ~isreal(fval)
        keyboard
    end
end

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Snoopy 2022-3-2

编辑：Snoopy 2022-3-2

OK. So "Objective function returned complex; trying a new point..." is not an error and MATLAB will not pause when this warning is displayed.

Walter Roberson 2022-3-2

suggest you add a conditional breakpoint to trigger if any(imag(VALUE))

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