Error using fittype for model evaluation

I want to find k1-k7 from this equation logKap= log(k1[Fe2+] + k2[FeOH+] + k3[Fe(OH)2] + k4[Fe(OH)3-] + k5[ FeCl+] + k6[ FeSO4] + k7[FeHSO4+]

I have data for [Fe species] and logKap from 40 experiments.

here are my code

clc;
clear;
close all;
% Import data
data = xlsread('Rateconstant.xlsx');
logKap = data(:,2);
deltalogKap = data(:,3);
Fe2_plus = data(:,4);
FeOH_plus = data(:,5);
FeOH2 = data(:,6);
FeOH3_minus = data(:,7);
FeCl_plus = data(:,8);
FeSO4 = data(:,9);
FeHSO4_plus = data(:,10);
n = 10;
% Create arrays to store the fitted parameters
k1 = zeros(1, n);
k2 = zeros(1, n);
k3 = zeros(1, n);
k4 = zeros(1, n);
k5 = zeros(1, n);
k6 = zeros(1, n);
k7 = zeros(1, n);
% Create arrays to store generated data
logKap2 = zeros(size(logKap, 1), n);
for i = 1:n
    
    % Generate new random data  within the range of Kap +- deltaKap
    logKap2(:,i) = logKap + deltalogKap.*(2*rand(size(logKap)) - 1);
    % Define the function to be fitted
    Model1= fittype('log10(k1*(Fe2_plus) + k2*(FeOH_plus) + k3*(FeOH2) + k4*(FeOH3_minus) + k5*(FeCl_plus) + k6*(FeSO4) + k7*(FeHSO4_plus))', 'independent', {'Fe2_plus', 'FeOH_plus','FeOH2','FeOH3_minus','FeCl_plus','FeSO4','FeHSO4_plus'}, 'dependent', 'logKap2');
    fitted1 = fit([Fe2_plus(:,i), FeOH_plus(:,i), FeOH2(:,i), FeOH3_minus(:,i), FeCl_plus(:,i), FeSO4(:,i), FeHSO4_plus(:,i)], logKap2(:,i), Model1, 'Lower', [0, 0, 0,0,0,0,0], 'Upper', [Inf, Inf, Inf,Inf,Inf,Inf,Inf]);
    % Record the fitted parameters
    k1(i) = fitted1.k1;
    k2(i) = fitted1.k2;
    k3(i) = fitted1.k3;
    k4(i) = fitted1.k4;
    k5(i) = fitted1.k5;
    k6(i) = fitted1.k6;
    k7(i) = fitted1.k7;
end

But I have some error from the fitting process and don't know how to fix it.

Error using fittype/testCustomModelEvaluation

Expression log10(k1*(Fe2_plus) + k2*(FeOH_plus) + k3*(FeOH2) + k4*(FeOH3_minus) + k5*(FeCl_plus) +

k6*(FeSO4) + k7*(FeHSO4_plus)) is not a valid MATLAB expression, has non-scalar coefficients, or

cannot be evaluated:

Not enough inputs to FITTYPE function.

Error in fittype>iCreateFittype (line 373)

testCustomModelEvaluation( obj );

Error in fittype (line 330)

obj = iCreateFittype( obj, varargin{:} );

Error in Rateconstant (line 37)

Model1= fittype('log10(k1*(Fe2_plus) + k2*(FeOH_plus) + k3*(FeOH2) + k4*(FeOH3_minus) + k5*(FeCl_plus) + k6*(FeSO4) + k7*(FeHSO4_plus))', 'independent', {'Fe2_plus', 'FeOH_plus','FeOH2','FeOH3_minus','FeCl_plus','FeSO4','FeHSO4_plus'}, 'dependent', 'logKap2');

Caused by:

Error using fittype/evaluate>I_ERROR_FCN_

Not enough inputs to FITTYPE function.

[the cyclist]

I'm very confused about why you are looping over your data 10 times, and why you are generating "new random data". This makes no sense to me.

Perhaps you could share the data, and also describe (or provide a reference to) the method you want to use to fit your data.

[Sarawud Saleesongsom]

I'm trying to do Monte Carlo simulation here. I want to take into account my error (deltalogKap) into logKap.

Answer 1

[Walter Roberson]

You cannot use nonscalar coefficients in the fit model. Your Fe2_plus and so on are nonscalar.

The computing model is that the fitting process can pass in variable-length of the independent variables, and that the result has to be the same size as the input. Normally all of the independent data is passed in, but potentially different size of data is passed in during the start-up phase when the expression is being probed for suitability.