title: How to isolate the exponent in Sympy (how to `match` large formulas in Sympy)
body: <p>I am trying to extract the exponent in formulas that resemble the Gaussian PDF, in form of <code>F*exp(E)</code>. The function <code>match()</code> from SymPy works for simple cases but not for more complicated formulas such as below.</p>
  
  <pre><code>from __future__ import division
  from sympy import *
  
  δ, b, σ, m, s, μ, x = symbols('δ b σ m s μ x', real=True)
  
  gauss = 1/σ/sqrt(2*pi)*exp( -(x-μ)**2/σ/σ/2 )
  big = sqrt(2*σ**2*x + 2*s**2)* exp(
          b**2/(2*x*(σ**2*x + s**2)) - b**2/(2*x*s**2) - b*μ/(σ**2*x + s**2) + b*δ/s**2 + μ**2*x/(2*σ**2*x + 2*s**2) - μ**2/(2*σ**2) + μ*δ/σ**2 - x*δ**2/(2*s**2) - δ**2/(2*σ**2)
      ) / (2*sqrt(pi)*σ*s)
  
  F, E = Wild('F', exclude=[exp,]), Wild('E', exclude=[exp,])
  pprint( gauss)
  print("match:")
  pprint( gauss.match(F*exp(E)))
  pprint( big )
  print("match:")
  pprint( big.match(F*exp(E)))  # Fails to match and returns None.
  </code></pre>
  
  <p>The formula for <code>big</code> is obviously in the form of F*exp(E) but <code>match()</code> does not work on it. How can I extract the exponent and the normalisation factor from Gauss-like formulas?</p>
  
  <p>How can I isolate the exponent in an equation with <code>exp()</code>?</p>