code: def logsumexp(
      a, axis=None, b=None, keepdims=False, return_sign=False
  ):
      """Compute the log of the sum of exponentials of input elements.
  
      Parameters
      ----------
      a : array_like
          Input array.
      axis : None or int or tuple of ints, optional
          Axis or axes over which the sum is taken. By default `axis` is None,
          and all elements are summed.
  
          .. versionadded:: 0.11.0
      keepdims : bool, optional
          If this is set to True, the axes which are reduced are left in the
          result as dimensions with size one. With this option, the result
          will broadcast correctly against the original array.
  
          .. versionadded:: 0.15.0
      b : array-like, optional
          Scaling factor for exp(`a`) must be of the same shape as `a` or
          broadcastable to `a`. These values may be negative in order to
          implement subtraction.
  
          .. versionadded:: 0.12.0
      return_sign : bool, optional
          If this is set to True, the result will be a pair containing sign
          information; if False, results that are negative will be returned
          as NaN. Default is False (no sign information).
  
          .. versionadded:: 0.16.0
  
      Returns
      -------
      res : ndarray
          The result, ``np.log(np.sum(np.exp(a)))`` calculated in a numerically
          more stable way. If `b` is given then ``np.log(np.sum(b*np.exp(a)))``
          is returned.
      sgn : ndarray
          If return_sign is True, this will be an array of floating-point
          numbers matching res and +1, 0, or -1 depending on the sign
          of the result. If False, only one result is returned.
  
      See Also
      --------
      numpy.logaddexp, numpy.logaddexp2
  
      Notes
      -----
      Numpy has a logaddexp function which is very similar to `logsumexp`, but
      only handles two arguments. `logaddexp.reduce` is similar to this
      function, but may be less stable.
  
      Examples
      --------
      >>> from scipy.special import logsumexp
      >>> a = np.arange(10)
      >>> np.log(np.sum(np.exp(a)))
      9.4586297444267107
      >>> logsumexp(a)
      9.4586297444267107
  
      With weights
  
      >>> a = np.arange(10)
      >>> b = np.arange(10, 0, -1)
      >>> logsumexp(a, b=b)
      9.9170178533034665
      >>> np.log(np.sum(b*np.exp(a)))
      9.9170178533034647
  
      Returning a sign flag
  
      >>> logsumexp([1,2],b=[1,-1],return_sign=True)
      (1.5413248546129181, -1.0)
  
      Notice that `logsumexp` does not directly support masked arrays. To use it
      on a masked array, convert the mask into zero weights:
  
      >>> a = np.ma.array([np.log(2), 2, np.log(3)],
      ...                  mask=[False, True, False])
      >>> b = (~a.mask).astype(int)
      >>> logsumexp(a.data, b=b), np.log(5)
      1.6094379124341005, 1.6094379124341005
  
      """
      a = _asarray_validated(a, check_finite=False)
      if b is not None:
          a, b = np.broadcast_arrays(a, b)
          if np.any(b == 0):
              a = a + 0.0  # promote to at least float
              a[b == 0] = -np.inf
  
      a_max = np.amax(a, axis=axis, keepdims=True)
  
      if a_max.ndim > 0:
          a_max[~np.isfinite(a_max)] = 0
      elif not np.isfinite(a_max):
          a_max = 0
  
      if b is not None:
          b = np.asarray(b)
          tmp = b * np.exp(a - a_max)
      else:
          tmp = np.exp(a - a_max)
  
      # suppress warnings about log of zero
      with np.errstate(divide="ignore"):
          s = np.sum(tmp, axis=axis, keepdims=keepdims)
          if return_sign:
              sgn = np.sign(s)
              s *= sgn  # /= makes more sense but we need zero -> zero
          out = np.log(s)
  
      if not keepdims:
          a_max = np.squeeze(a_max, axis=axis)
      out += a_max
  
      if return_sign:
          return out, sgn
      else:
          return out
  
imports: from __future__ import division, print_function, absolute_import
  import numpy
  from scipy._lib._util import _asarray_validated
label_desc: Use image node_id 1 for calling a global function with example usage: logsumexp(a, axis, b, keepdims, return_sign) and returns: out,  sgn, out