[Nek5000-users] How to obtain spectral coefficients and basis

[nek5000-users at lists.mcs.anl.gov]

Hello,

I'm trying to represent the solution, either velocity or temperature, in 
terms of spectral basis, i.e.

$u=\Sigma a_i \phi_i $ with $\phi_i$ as the basis and $a_i$ as the 
coefficients.

I have two questions:

1) (a naive one!) Which basis is being used in Nek5000? I assume it is 
Chebyshev polynomials. Is that true? If not, what is the basis?

2) How can I retrieve the coefficients $a_i$? Also, is there a way to 
access such coefficients during the solution, say by writing them to a file?

I really appreciate the responses. As a side note, I'd like to use DNS 
data for model reduction.

Many thanks,
Saleh