title: How to represent inf or -inf in Cython with numpy?
body: <p>I am building an array with cython element by element. I'd like to store the constant <code>np.inf</code> (or <code>-1 * np.inf</code>) in some entries. However, this will require the overhead of going back into Python to look up <code>inf</code>. Is there a <code>libc.math</code> equivalent of this constant? Or some other value that could easily be used that's equivalent to <code>(-1*np.inf)</code> and can be used from Cython without overhead?</p>
  
  <p><em>EDIT</em> example, you have:</p>
  
  <pre><code>cdef double value = 0
  for k in xrange(...):
    # use -inf here -- how to avoid referring to np.inf and calling back to python?
    value = -1 * np.inf
  </code></pre>