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Not enough input arguments.

Hi Everyone,
I have a user-defined code that is based on Euler method, that runs successfully. However the output does not compare satisfactority with the experiment for one variable. I would like to use fminsearch to estimate the parameters that can improve the fitting. However, when I try that I get the error message that states:
Error using fzero (line 306)
FZERO cannot continue because user-supplied function_handle ==> HionpH failed with the error below.
Not enough input arguments.
Error in ParametersFittingEulerMethodWater>EulerMethod (line 131)
pH = fzero(@HionpH, pH1);
Error in fminsearch (line 200)
fv(:,1) = funfcn(x,varargin{:});
Error in ParametersFittingEulerMethodWater (line 58)
[b, Results] = fminsearch(@EulerMethod,b);
I can not figure out which arguments are outstanding.
I have attached both the running code and the faulty code.
Please help

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Answer by Stephen Cobeldick on 23 Dec 2018
Edited by Stephen Cobeldick on 23 Dec 2018
 Accepted Answer

You defined the function HiopH with two input arguments:
function ph = HionpH (pH,b)
In earlier threads we helped you to parameterize it so that you could use fzero to find the pH value:
fzero(@(pH)HionpH(pH,b),pH_trial);
But now you tried to supply it to fzero again, without parameterizing it:
pH = fzero(@HionpH, pH1);
Do you notice the difference? HionpH requires two input arguments. fzero provides exactly one input argument. When fzero calls that function handle (of HionpH), does it provide the second input argument? (hint: no, it only provides one input argument). Thus the error.

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Thanks a lot Stephen. I realised those mistakes and rectified them.

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