title: Numexpr doesn't recognize float type (sparse matrix)
body: <p>I would like to evaluate the performance of numexpr module in python (2.7). For that purpose, I created a random sparse matrix of size (10^5, 10^5). However, the script below throws an error at the expression evaluation step already, saying that it doesn't recognize the object type. </p>
  
  <p>What am I doing wrong?</p>
  
  <p>Code:</p>
  
  <pre><code>import timeit
  import scipy.sparse as sps
  import numpy as np
  import numexpr as ne
  
  test_matrix = sps.rand(1e4, 1e4, density=0.01, format='coo', dtype = np.float32)
  ne.evaluate('sum(test_matrix, axis = 1)')
  
  setup = 'import numexpr as ne; import numpy as np'
  print min(timeit.Timer('ne.evaluate(sum(test_matrix, axis = 1))', setup=setup).repeat(7, 1000))
  </code></pre>
  
  <p>Error:</p>
  
  <p>Traceback (most recent call last):</p>
  
  <pre><code>File "benchmark_expressmath.py", line 19, in &lt;module&gt;
  ne.evaluate('sum(test_matrix, axis = 1)')
  File "C:\Users\blahblah\AppData\Local\Continuum\Anaconda\lib\site-packages\numexpr\necompiler.py", line 756, in evaluate
  signature = [(name, getType(arg)) for (name, arg) in zip(names, arguments)]
  File "C:\Users\blahblah\AppData\Local\Continuum\Anaconda\lib\site-packages\numexpr\necompiler.py", line 654, in getType
  raise ValueError("unknown type %s" % a.dtype.name)
  ValueError: unknown type object
  </code></pre>