plsrectify the error in my code

Error in MI_fitting (line 6)

field = mat1(:,1); % safer extraction, This is the error observed in my Matlab Code.

clc;
clear;
close all;
mat1 = readtable('mat1.txt');

Error using readtable (line 19)
Unable to find or open 'mat1.txt'. Check the path and filename or file permissions.

field = mat1(:,1);   % safer extraction
Z = mat1(:,2);
plot(field,Z,'bo');
hold on;
lb=[50,201,5e9,0.0001,8.1e-6,0.001,50];  
ub=[100,419,100e9,1,151e-6,21,71]; 
MI = lsqcurvefit(@impedance_test1,[85,391.29,20e9,5,16e-6,5,59.03],field,Z,lb,ub);
[fitdata,Mr] = impedance_test1(MI,field);
plot(field, fitdata,'-r','LineWidth',2);
xlabel('Field');
ylabel('MI');
legend('mat1','fitting')
title('MI vs Field')


function[modZ,Mr]=impedance_test1(var,field)

M=var(1);Ha=var(2);sig2=var(3);alpha=var(4);D=var(5);si=var(6);teta=var(7);

%Define constants

g=((2.2).*(10e5));
w=((2).*(10e6));
M0=((4).*(pi).*(10e-7));

c=3*(10e10);
l=3;
% Define function.

wm=g.*4.*(pi).*M;

w1=g.*((Ha.*(cosd(teta-si)).^2)+((field).*(sind(teta))));

w2=g.*((Ha.*(cosd(2.*(teta-si))))+((field).*(sind(teta))));

%Relative permeability

Mr=(wm.*(wm+w1-(1i.*(alpha).*w)))./(((wm+w1-(1i.*(alpha).*w)).*(w2-(1i.*(alpha).*w)))-(w.^2));

Mr=abs(Mr);

Mef=Mr.*M0;

T2=c./(sqrt(2.*(pi).*(sig2).*w));

Z=(((1-1i).*l).*(((sqrt(Mef+1)).*((sind(teta)).^2))+(cosd(teta)).^2)./((pi).*(sig2).*D.*T2));

modZ=((abs(Z)./(2.34401312390370e-09))-1).*100;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

end

0 121.58696

0.8 117.91178

1.6 114.23316

2.4 112.21164

3.2 110.54767

4 108.67398

4.8 105.74483

5.6 102.94633

6.4 100.21659

7.2 97.78595

8 95.7438

8.8 93.43005

9.6 91.32946

10.4 88.97446

11.2 86.53694

12 84.33321

12.8 82.17761

13.6 80.04263

14.4 77.99017

15.2 75.96177

16 73.95056

20 67.38405

24 59.11919

28 51.67944

32 45.06481

36 39.36466

40 34.35555

44 29.97903

48 26.08382

52 22.6321

56 19.59982

60 16.87008

64 14.38443

68 12.16007

72 10.14886

76 8.29924

80 6.62495

84 4.54155

88 3.62017

92 2.31375

96 1.12421

[Rik]

Try to make a MWE so we can run your code without any other dependencies and can reproduce your issue. The best way to do this is to use the code section in the editor and use the run button. That way you can make sure we will see the same error message as you do.

Answer 1

[Stephen23]

The error occurs because READTABLE returns a table object, and you cannot extract the content from a table using parentheses like mat1(:,1). With tables, you need to use curly brackets {} or dot notation if you want the content e.g. as a numeric array. This is explained here:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

Alternatively you could skip the table entirely and simply import the data as a numeric matrx using e.g. READMATRIX.

With the correct table indexing the code works without error:

% Read table:
mat1 = readtable('mat1.txt');

% Extract data as numeric arrays:
field = mat1{:,1};
Z     = mat1{:,2};

% Plot experimental data:
plot(field, Z, 'bo');
hold on;

% Boundaries for fit
lb = [50, 201, 5e9, 0.0001, 8.1e-6, 0.001, 50];
ub = [100, 419, 100e9, 1, 151e-6, 21, 71];

% Fitting:
MI = lsqcurvefit(@impedance_test1, [85, 391.29, 20e9, 5, 16e-6, 5, 59.03], field, Z, lb, ub);

Local minimum possible.

lsqcurvefit stopped because the final change in the sum of squares relative to 
its initial value is less than the value of the function tolerance.

% Generate fitted data:
[fitdata, Mr] = impedance_test1(MI, field);

% Plot fit:
plot(field, fitdata, '-r', 'LineWidth', 2);

% Plot settings:
xlabel('Field');
ylabel('MI');
legend('mat1', 'fitting');
title('MI vs Field');

% Fitting function:
function [modZ, Mr] = impedance_test1(var, field)
    M     = var(1);
    Ha    = var(2);
    sig2  = var(3);
    alpha = var(4);
    D     = var(5);
    si    = var(6);
    teta  = var(7);

    % Define constants
    g  = 2.2 * 1e5;
    w  = 2 * 1e6;
    M0 = 4 * pi * 1e-7;
    c  = 3 * 1e10;
    l  = 3;

    % Intermediate calculations:
    wm = g * 4 * pi * M;
    w1 = g * (Ha * (cosd(teta - si)).^2 + field * sind(teta));
    w2 = g * (Ha * (cosd(2 * (teta - si))) + field * sind(teta));

    % Relative permeability:
    Mr = (wm .* (wm + w1 - 1i * alpha * w)) ./ ...
         ((wm + w1 - 1i * alpha * w) .* (w2 - 1i * alpha * w) - w^2);

    Mr = abs(Mr);
    Mef = Mr * M0;

    T2 = c / sqrt(2 * pi * sig2 * w);

    Z = ((1 - 1i) * l) .* ((sqrt(Mef + 1) .* (sind(teta).^2)) + (cosd(teta).^2)) ...
        ./ (pi * sig2 * D * T2);

    modZ = ((abs(Z) / 2.34401312390370e-09) - 1) * 100;
end