Re: make_lsq_spline and conversion to float

Hi,

Several reasons, in fact. First and foremost, linear algebra is
delegated to LAPACK, which only works in floating point. If you're
using integer values so large that the conversion to float64 is lossy,
essentially any integer arithmetics is nearly guaranteed to overflow.
So, the computations should stay in floating-point. There might be a
case for preserving float32 dtypes, but so far no use case was
reported, so it's separate.

All in all, you're best off shifting and scaling the inputs yourself.
I'm actually surprised why this makes things slow : this is only O(N),
while the linear algebra part should definitely be more costly.

Cheers,

Evgeni

On Tue, Oct 26, 2021 at 9:21 AM Thomas Hilger <[email protected]> wrote:
>
> Hello,
>
> When using make_lsq_spline(x,y,t) with x being int64, I am running into the issue that the x-array is internally converted to float. While on an int64-level the input x-values are ordered, after the internal conversion to float, an exception is raised, because as a result some of these values are identical to each other.
>
> I was wondering about the reason for that internal conversion to float (it seems to reside only in handling complex dtypes or is there some other mechanism in Cox-de-Bor algorithm or Cholesky?). It is not obvious to me.
>
> Right now I can solve this problem by shifting the x-values, such that the numbers are smaller and the conversion does not harm this way. However, this makes things really slow or very unhandy codewise.
>
> Maybe it is feasible to modify _get_dtype a little?
>
> Thanks and cheers,
> Thomas.
> _______________________________________________
> SciPy-User mailing list -- [email protected]
> To unsubscribe send an email to [email protected]
> https://mail.python.org/mailman3/lists/scipy-user.python.org/
> Member address: [email protected]
_______________________________________________
SciPy-User mailing list -- [email protected]
To unsubscribe send an email to [email protected]
https://mail.python.org/mailman3/lists/scipy-user.python.org/
Member address: [email protected]