help: I need to solve the problem of the function "lsqcurvefit" I have an error when I started to run the program

Hello,

I have an error in the function "lsqcurvefit" that I have to use, I tried to solve the problem but I don't know what the error is exactly, I have to know that I respect the syntax of the function.?

Thank you for your help

[Sachin]

Could you please provide more information or Code ?

[Sou Fat]

this is : the part of the code

i need to find in this function the variable x(1) and x(2) . the data i have is xdata which is a vector colonne size(275) and ydata the same size and also it's vector colonne.

Kj=1.0*10-6
Kth=0.001
% fun=@(x,xdata)(a+b.*(C1-C2))
fun=@(x,xdata)( (((x(1).*Kj.*Kth+x(2).*Kj))./((-(Kth+x(1).*Kth+x(2))-sqrt((Kth+x(1).*Kth+x(2)).^2-4.*x(2).*Kth)).*(-(Kth+x(1).*Kth+x(2))+sqrt((Kth+x(1).*Kth+x(2)).^2-4.*x(2).*Kth)))) +  ((x(1).*Kth.*Kj+x(2).*Kj)./(-sqrt((Kth+x(1).*Kth+x(2)).^2-4.*Kth.x(2)))).* (       ((exp((-(Kth+x(1).*Kth+x(2))-sqrt((Kth+x(1).*Kth+x(2)).^24.*Kth.*x(2))).*Duree))./ (-(Kth+Kth.*x(1)+x(2))-sqrt((Kth+x(1).*Kth+x(2)).^2-4.*Kth.*x(2))))- ( (exp((-(Kth+x(1).*Kth+x(2))+sqrt((Kth+x(1).*Kth+x(2)).^2-4.*Kth.*x(2))).*Duree))./ (-(Kth+Kth.*x(1)+x(2))+sqrt((Kth+x(1).*Kth+x(2)).^2-4.*Kth.*x(2)))) )       )
x0=[100 ,-1]
%x=lsqcurvefit(fun,x0,xdata,ydata)
%Xdata=[xdata Courant]
x=lsqcurvefit(fun,x0,xdata,ydata)
Kthcbox= x(2)
Xcpcbox= x(1)

[Torsten]

Neither the array "xdata" nor the array "ydata" appear in the definition of your function "fun". That's why you have only a single equation for the unknown vector x. I doubt this is what you want.

[Sou Fat]

xdata appear in the function like the time (beacuse i wrote in the top of the programme the xdata=Duree) but ydata i declareted also but i can't use in the function .

my function is : T(t)=A+b.*(C1-C1) which C1 et C2 depend the time.

I need to find the values of x to fit the "fun" function to the ydata.?

so i don't know exactely the probleme ?

Answer 1

[Cris LaPierre]

The error message mentions 'dot indexing', which means you have likely forgotten a multiplication symbol in your equation. I found this about halfway through your equation: Kth.x(2)

You probably meant to do elementwise multiplication: Kth.*x(2)

[Sou Fat]

I corrected it but I have another error :

"Error using snls (line 47)

Objective function is returning undefined values at initial point. lsqcurvefit cannot continue.

Error in lsqncommon (line 167)

snls(funfcn,xC,lb,ub,flags.verbosity,options,defaultopt,initVals.F,initVals.J,caller, ...

Error in lsqcurvefit (line 271)

lsqncommon(funfcn,xCurrent,lb,ub,options,defaultopt,allDefaultOpts,caller,...

Error in fun_cfd_1 (line 21)

x=lsqcurvefit(fun,x0,xdata,ydata)"

[Cris LaPierre]

Reading the error message will tell you what is wrong.

It would appear your objective function is undefined at x0. Pick a different start value.

It's hard for us to help more than this without having access to your data. Consider saving your variables to a mat file and attaching it to your post, along with your script.

[Sou Fat]

Sorry for my late answer, but I dont know exactly how to save data from Excel to matlab(.mat). I m searching how I can do it

[Cris LaPierre]

I linked to the corresponding page in the documentation.

You could also just attach your excel file using the paperclip icon, but you also need to then share the code that loads that spreadsheet as well as the code that creates the variables used when calling lsqcurvefit.

[Sou Fat]

Thank you for your answer, I found how savibg the variables to à mat file.