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Function value at starting guess must be finite and real

Hi everyone,
I know that the question is self-explaning. I am supriced that I get this error:
Error using fzero (line 328)
Function value at starting guess must be finite and real.
Error in SlurryCase08Feb2019a>SO2_OdeDriver (line 218)
pH = fzero(@(pH)HionpH(pH,b),pH_trial);
Error in SlurryCase08Feb2019a>kinetics (line 164)
y = SO2_OdeDriver(y0,b);
Error in lsqcurvefit (line 213)
initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});
Error in SlurryCase08Feb2019a (line 73)
Caused by:
Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.
Even after ensuring that all all my initial guesses are finite and real. I have checked my code (attached) thoroughly, but I can't find my mistake.
Please help.

  댓글 수: 2

Hi Dursman,
The initial guesses may be finite and real, but the error message says that the value of the function at the initial guess is not finite and real. HionpH depends on three global variables (definitely not recommended practice) as well as its input argument, but if you go to the debugger you should be able to track this down.
Thank you somuch. I now understand better.

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답변 수: 1

Steven Lord 님의 답변 8 Feb 2019
 채택된 답변

As David said, fzero is complaining about the value of your function at the initial guess. A simpler example illustrating the problem:
f = @(x) (1./x)-1;
initialGuess = 0;
fzero(f, initialGuess)
While initialGuess is finite and real, the same cannot be said for the value of f evaluated at initialGuess.
If I change my initial guess to something where f(newInitialGuess) is finite and real, fzero can find a solution.
newInitialGuess = 2;
x = fzero(f, newInitialGuess)

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Thank you somuch. I now understand.

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