Re: change in polyfit()'s behaviour?

[Ben Abbott]

On Jan 3, 2009, at 11:47 AM, Thomas Weber wrote:

> Hi,
>
> the following raises in error in the 3.0 branch:
>         
>         polyfit ([1,2; 3,4], [1,2; 3,4],4)
> namely
> error: polyfit: x and y must be vectors of the same size
>
> In fact, this error is part of test_poly.m in the test/ subdirectory.
>
>
> In the development sources, the test has been removed and the output  
> is
> now:
>
> octave:1> polyfit ([1,2; 3,4], [1,2; 3,4],4)
> ans =
>
>   0.011358  -0.113585   0.397547   0.432076   0.272603
>
> Is this change intentional, ie should polyfit handle matrices as input
> arguments?
>
>         Thomas

It is compatible behavior, so it should accept matrices, provided they  
are the same size.

>>  polyfit ([1,2; 3,4], [1,2; 3,4],4)
Warning: Polynomial is not unique; degree >= number of data points.
> In polyfit at 72

ans = [0.02   -0.2    0.7      0   0.48]

It *may* be sensible to add the warning regarding the equations  
exceeding the unknowns. However, QR calculates the minimum-norm which  
I understand is unique. So I'm inclined to leave it as it is.

Ben