I am a beginner to matlab. kindly help me with the error "Error using fit_simp (line 2) Not enough input arguments".

i was trying to write the code by transforming the answr given at the link http://www.mathworks.com/matlabcentral/answers/97439-how-do-i-fit-an-arbitrary-function-to-data-using-lsqnonlin-in-optimization-toolbox to my situation and i got the error as above. help me please to run this code. i want to do non linear least square minimization using levenberg marquardt method.

function diff = fit_simp(x,t,s)

Q=x(1);

T=x(2);

r=x(3);

S=x(4);

diff = ((Q/4/pi/T)*(-0.5772-log(r^2*S/4/T/t)+(r^2*S/4/T/t)-(r^2*S/4/T/t)/4)-s);

t = [1 2 3 4 5 7 9 15 20 30 40 50 70 90 130 160 200 240];

s = [0.89 .81 .76 .68 .64 .56 .49 .55 .38 .34 .28 .21 .17 .14 .10 .08 .05 0.03];

x0 = [.1;500;1;.05]';

x=lsqnonlin(@fit_simp,x0,[],[],[],t,s);

Y_new = (x(1)/4/pi/x(2))*(-0.5772-log(x(3)^2*x(4)/4*x(2)*t)+(x(3)^2*x(4)/4*x(2)*t)-(x(3)^2*x(4)/4*x(2)*t)/4);

plot(t,s,'+r',t,Y_new,'b');

Answer 1

[Stalin Samuel]

start with file 'main.m'

Answer 2

[Walter Roberson]

The example there is quite outdated. You need

x = lsqnonlin(@(x) fit_simp(x,t,s),x0,[],[],[]);

Also, you should not name a variable "diff" as that is confusing and interfers with the use of the diff() function.

Make sure that your lines from t = [....] onward are in a different file, not in fit_simp.m . For example you could put those lines to the end into fit_driver.m and then you would invoke fit_driver in order to run the code