Python: Why isn't this working?/What does this error really mean?

Question

I've currently got the following, but it won't iterate over i. I don't understand why it isn't working. Bwavelength and throughput are lists. It appears that i starts at 0, but won't increase to 1.

ABconstant=[]

c=3e18
for i in range(0, ((len(Bwavelength))-1)):
    ABconstant1=(((3e18/((Bwavelength[i])**2))*throughput[i]))
    ABconstant.append(ABconstant1)
    i+=1
    a=Bwavelength[0]
    b=Bwavelength[-1]
    h=((b-a)/len(Bwavelength))
    ABflux = numpy.trapz(Bwavelength, ABconstant, h)
return ABflux

The error I get is:

Traceback (most recent call last):
  File "Rewrite17.11.2014.py", line 196, in <module>
    ABflux1 = ABconversion(Bwavelength, throughput)
  File "Rewrite17.11.2014.py", line 186, in ABconversion
    ABflux = numpy.trapz(Bwavelength, ABconstant, h)
  File "C:\Python27\lib\site-packages\numpy\lib\function_base.py, line 3234, in trapz
    ret = add.reduce(d * (y[slice1]+y[slice2]/2.0, axis)
ValueError: Operands could not be broadcast together with shapes (0,) (444,)

Bwavelength and throughput are of equal length.

I have no idea what that actually means, despite having looked it up.

Thanks in advance.

Bwavelength and throughput are the same length, so surely ABconstant should be the same length if i iterates over the length of Bwavelength? — NXW, Nov 22 '14 at 18:49

score 2 · Accepted Answer · answered Nov 22 '14 at 19:06

2

The loop can be substituted by vector calculations:

c=3e18
ABconstant = c / numpy.array(Bwavelength) ** 2 * throughput
ABflux = numpy.trapz(ABconstant, Bwavelength)
return ABflux

answered Nov 22 '14 at 19:06

Daniel

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I think that you have corrected, in just two lines, a not trivial number of mistakes in the OP code... – gboffi Nov 22 '14 at 20:14

Python: Why isn't this working?/What does this error really mean?

1 Answers1