Weighting data in datafit

[zugvogel]

Hello,
I'm having a lot of trouble figuring out how to weight data-points for
fitting using "datafit".

I have:
[p,err]=datafit(G,ndata,W,p0)

The function G is:
function e=G(p, z), // output is "e", input "p" and "z"
    y=z(1),x=z(2); // y is the top row, x bottom
    e=y-FF(x,p), // optimise to zero, FF is my function
endfunction

ndata is 2 rows and 12 columns, the top row being y-axis values and the
bottom row being x-axis values

p0 is 4 rows and 1 column.

W is my weighting matrix. I set this initially as just a 12x12 identity
matrix.

I just can't get this to work however. I keep getting:

-------------------
-->[p,err]=datafit(G,ndata,W,p0)
 !--error 15 
Submatrix incorrectly defined.

at line      26 of function costf called by :  
at line     174 of function datafit called by :  
[p,err]=datafit(G,ndata,W,p0)
-------------------

Can anyone help me? I have tried changing W in many ways but I can't get it
to work.
The help section on datafit says W should be of size ne x ne, where G is
size ne x 1. I assume ne is the same as nz (ie, 12, the number of data
points) but maybe this is wrong? In any case I tried make ne=1,2,3...12
(always a square matrix) but without success. If I do it without weighting,
it works.

I would really appreciate any help. I'm completely out of ideas.

Thank you!

Tom

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