[Numpy-discussion] Vectorize or rewrite function to work with array inputs?

DParker at chromalloy.com DParker at chromalloy.com
Mon Jan 31 10:15:59 EST 2011

```I have several functions like the example below that I would like to make
compatible with array inputs. The problem is the conditional statements
give a ValueError: The truth value of an array with more than one element
is ambiguous. Use a.any() or a.all(). I can use numpy.vectorize, but if
possible I'd prefer to rewrite the function. Does anyone have any advice
the best way to modify the code to accept array inputs? Thanks in advance
for any assistance.

NAN = float('nan')

def air_gamma(t, far=0.0):
"""
Specific heat ratio (gamma) of Air/JP8
t - static temperature, Rankine
[far] - fuel air ratio [- defaults to 0.0 (dry air)]
air_gamma - specific heat ratio
"""
if far < 0.:
return NAN
elif far < 0.005:
if t < 379. or t > 4731.:
return NAN
else:
air_gamma = -3.472487e-22 * t ** 6. + 6.218811e-18 * t ** 5. -
4.428098e-14 * t ** 4. + 1.569889e-10 * t ** 3. - 0.0000002753524 * t **
2. + 0.0001684666 * t + 1.368652
elif far < 0.069:
if t < 699. or t > 4731.:
return NAN
else:
a6 = 4.114808e-20 * far ** 3. - 1.644588e-20 * far ** 2. +
3.103507e-21 * far - 3.391308e-22
a5 = -6.819015e-16 * far ** 3. + 2.773945e-16 * far ** 2. -
5.469399e-17 * far + 6.058125e-18
a4 = 4.684637e-12 * far ** 3. - 1.887227e-12 * far ** 2. +
3.865306e-13 * far - 4.302534e-14
a3 = -0.00000001700602 * far ** 3. + 0.000000006593809 * far
** 2. - 0.000000001392629 * far + 1.520583e-10
a2 = 0.00003431136 * far ** 3. - 0.00001248285 * far ** 2. +
0.000002688007 * far - 0.0000002651616
a1 = -0.03792449 * far ** 3. + 0.01261025 * far ** 2. -
0.002676877 * far + 0.0001580424
a0 = 13.65379 * far ** 3. - 3.311225 * far ** 2. + 0.3573201 *
far + 1.372714
air_gamma = a6 * t ** 6. + a5 * t ** 5. + a4 * t ** 4. + a3 *
t ** 3. + a2 * t ** 2. + a1 * t + a0
elif far >= 0.069:
return NAN
else:
return NAN
return air_gamma

David Parker
Chromalloy - TDAG
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20110131/0bec51bf/attachment.html>
```