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

DParker@chromallo... DParker@chromallo...
Tue Feb 1 13:22:16 CST 2011


Thanks for the advice. 

Using Sebastian's advice I was able to write a version that worked when 
the input arguments are both arrays with the same length. The code 
provided by eat works when t is an array, but not for an array of far. 

The numpy.vectorize version works with any combination of scalar or array 
input. I still haven't figured out how to rewrite my function to be as 
flexible as the numpy.vectorize version at accepting either scalars or 
array inputs and properly broadcasting the scalar arguments to the array 
arguments. 

David Parker 
Chromalloy - TDAG



From:   eat <e.antero.tammi@gmail.com>
To:     Discussion of Numerical Python <numpy-discussion@scipy.org>
Date:   01/31/2011 11:37 AM
Subject:        Re: [Numpy-discussion] Vectorize or rewrite function to 
work with array inputs?
Sent by:        numpy-discussion-bounces@scipy.org



Hi,

On Mon, Jan 31, 2011 at 5:15 PM, <DParker@chromalloy.com> wrote:
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.
 
If I understod your question correctly, then air_gamma could be coded as:
def air_gamma_0(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:
        ag= air_gamma_1(t)
        ag[np.logical_or(t< 379., t> 4731.)]= NAN
        return ag
    elif far< 0.069:
        ag= air_gamma_2(t, far)
        ag[np.logical_or(t< 699., t> 4731.)]= NAN
        return ag
    else: 
        return NAN 
Rest of the code is in the attachment.
 
 
My two cents,
eat



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
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