code: def sigma2fwhm(sigma):
      """Convert a sigma in a Gaussian kernel to a FWHM value
  
      Parameters
      ----------
      sigma : array-like
         sigma value or values
  
      Returns
      -------
      fwhm : array or float
         fwhm values corresponding to `sigma` values
  
      Examples
      --------
      >>> fwhm = sigma2fwhm(3)
      >>> fwhms = sigma2fwhm([3, 4, 5])
      >>> fwhm == fwhms[0]
      True
      """
      sigma = np.asarray(sigma)
      return sigma * np.sqrt(8 * np.log(2))
  
file_path: nipy/nipy/algorithms/kernel_smooth.py
imports: import gc
  import numpy
  import numpy.linalg
  from numpy import fft
  from nipy.core.api import AffineTransform, Image
  from nipy.core.reference.coordinate_map import product
  from nipy.utils import seq_prod
label_desc: Use image node_id 2 for calling a global function with example usage: sigma2fwhm(sigma) and returns: unknown