# Last edited on 2021-07-31 15:29:11 by jstolfi

from math import sqrt

def basis_sampled_residuals_combine(R, w):
  # Given a list of vectors of floats,
  # as produced by {basis_samples_residuals_compute},
  # combines them into a single vector by the Euclidean norm;
  # or, if {w} is not {None}, by the {w}-weighted norm.
  
  nf = len(R);
  assert nf > 0, "no residuals to combine"
  ns = len(R[0])
  
  e = []
  for ks in range(ns):
    sum_r2 = 0;
    for kf in range(nf):
      rfs = R[kf][ks]
      ws = 1 if w == None else w[ks]
      sum_r2 += rfs*rfs*ws
    es = sqrt(sum_r2)
    e.append(es)
  return e
  # ----------------------------------------------------------------------