Function value and YDATA sizes are not equal BUT THEY ARE

Hi everyone,

I have a problem when I try to fit a non-linear function. The message I received says: FUNCTION VALUE AND Y DATA SIZES ARE NOT EQUAL"

BUT I already checked those sizes and seems to be equal. I don't know what is the problem. Hope somebody could help me.

This is the code:

%REFERENCE:
% "The physical chemistry of high-sensitivity differential scanning
% calorimetry of biopolymers" by Stephen Leharne in ChemTexts (2017)
% 3:1 [DOI 10.1007/s40828-016-0038-0]
clc, clear;
%--------------------------------- INPUT ---------------------------------
Data_Fig_7 = [303.58, 0.09
    304.55, 0.56
    305.56, 1.05
    306.52, 1.48
    307.52, 1.96
    308.51, 2.56
    309.43, 3.06
    310.41, 3.55
    311.43, 4.17
    312.37, 4.76
    313.36, 5.31
    314.36, 5.95
    315.39, 6.58
    316.38, 7.14
    317.36, 7.96
    318.23, 8.46
    318.94, 9.24
    319.89, 10.01
    320.80, 10.74
    321.37, 11.47
    322.08, 12.47
    322.91, 13.69
    323.48, 14.77
    323.91, 15.72
    324.31, 16.88
    324.85, 18.19
    325.36, 19.83
    325.88, 21.70
    326.39, 23.75
    326.91, 26.10
    327.43, 28.53
    327.98, 31.62
    328.50, 34.80
    329.02, 38.64
    329.53, 42.51
    330.05, 46.64
    330.47, 50.58
    330.98, 54.15
    331.50, 57.44
    332.11, 59.66
    332.82, 60.80
    333.58, 60.23
    333.55, 59.76
    334.12, 57.88
    334.64, 54.67
    335.15, 50.73
    335.71, 46.63
    336.21, 42.70
    336.63, 39.12
    337.17, 35.88
    337.68, 33.13
    338.20, 30.93
    338.71, 28.90
    339.23, 27.30
    339.74, 26.15
    340.30, 25.23
    341.00, 23.92
    341.79, 23.11
    342.69, 22.58
    343.68, 22.23
    344.67, 21.96
    345.67, 21.77
    346.66, 21.70
    347.66, 21.63
    348.64, 21.56
    349.62, 21.48
    350.61, 21.49
    351.59, 21.51
    352.52, 21.48
    353.50, 21.47
    354.50, 21.41
    355.49, 21.32
    356.46, 21.34
    357.47, 21.32
    358.46, 21.32
    359.46, 21.11
    360.47, 21.06
    361.45, 20.93
    362.26, 20.98];

Hvh = 400; %kJ mol-1
Hcal = 300; %kJ mol-1
R = 0.00831; %kJ mol-1 K-1
Tr = 332.4; %K Obtained form the Table 2
cp = 20; %kJ mol-1 Obtained from the Fig 7 
%------------------------------- Calculations -----------------------------
%Figure 7
T7 = Data_Fig_7(:,1);
Cp7 = Data_Fig_7(:,2);
x(1) = Hvh; 
x(2) = Hcal;
%K0 = 1*exp(-((x(1)/R) * (1./T7 + 1/Tr)) + ((cp/R)*((log(T7./Tr))-1+(Tr./T7))))
%fD0 = K0./(1+K0)
%Cp0 = ((x(1)*x(2))./(R.*(T7).^2)) .* (fD0.*(1-fD0)) + (fD0.*(x(2)/x(1))*cp)
K = @(T7,x) 1*exp(-((x(1)/R) * (1./T7 + 1/Tr)) + ((cp/R)*((log(T7./Tr))-1+(Tr./T7))))
Ka = K(T7,x)
fD = @(T7,x) K(T7,x)./(1+K(T7,x))
fDa = fD(T7,x)
Cp = @(T7,x) ((x(1)*x(2))./(R.*(T7).^2)) .* (fD(T7,x).*(1-fD(T7,x))) + (fD(T7,x).*(x(2)/x(1))*cp)
Cpa = Cp(T7,x)
[x,resnorm,~,exitflag,output] = lsqcurvefit(Cp,x,T7,Cp7)

Answer 1

[John D'Errico]

The expectation is that in the function (here, Cp) the data vector should be the SECOND argument.

It needs to be

Cp = @(x,T7) ((x(1)*x(2))./(R.*(T7).^2)) .* (fD(T7,x).*(1-fD(T7,x))) + (fD(T7,x).*(x(2)/x(1))*cp);

If you are not sure, read the help.

min  sum {(FUN(X,XDATA)-YDATA).^2}  where X, XDATA, YDATA and the
  X                                 values returned by FUN can be 
                                   vectors or matrices.

So the first argument to fun should have been x, and the second argument T7. MATLAB cares about the sequence you provide the arguments. :)

[Leonardo Gómez]

Thank you for answering ! It is working now! I completely missed that order.