Re: regarding leasqr

[Martijn]

Hi Preeti,
I did not look into your formula's but I have the impression that a
number of parameters are 100% correlated and therefore impossible to
determine. A simple example: fitting f(x,p) = p(1)*exp(p(2)*x + p(3)) to
a set of data will fail because p(1) and p(3) are correlated: increasing
p(3) with 1 has the same effect as multiplying p(1) with e. It is
therefore impossible to determine them from a fit.

Your problem might be similar.

Good luck,

Martijn

On Mon, 2011-07-04 at 14:48 +0200, preeti gaikwad wrote:
> 
>  
> Hello all, 
> 
>               I am the new user in fitting please help me to solve my
> query. I am using leasqr to estimate parameters from the experimental
> data. 
> 
> my fuction is 
> 
> 
> s=A.*exp(-x./tabs).*(D./D0).^2.*exp(-(pi*pi).*(D.*x)./L.^2);
> 
> where D is 
> 
> D=(D0.*tloc.^(a))./(tloc.^(m).+x.^(m)).^(a./m);
> 
> I would like to calculate 
> 
> 
> 
> A = p(6);% constant value 
> 
> D0=p(2); 
> 
> tloc=p(3);
> 
> a=p(4);
> 
> m=p(5);
> 
>  Using the leasqr 
> 
> 
> [f, p] = leasqr(t, y, pin,'conv_fnc', tolerance, max_iterations,
> weights, dp, dFdp, options);
> 
> unfortunately i am getting value whatever is my pin 
> 
> 
> like my pin is 
> 
> pin = [0.5 25 0.000000005 1 7 1000 0]
> 
> 
> and for all value of x I have straight line like but my experimental
> data is exponential decreasing function. 
> 
> 
> 
> and the defined fuction is s also exponential decay function. My quest
> is why leasqr is not giving the new calculated value from the fun
> s???? THANKS FOR YOUR HELP in advance. 
> 
> 
> 
> regards P
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