When applying function to array, Error "ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()"

Question

I used scipy.integrate to get the value of the Fresnel integrals, and I now wish to plot the Cornu spiral. However, when I attempt to create an array with the value of the integral for multiple inputs, I get the error mentioned in the title. I can't see how what I'm doing has anything to do with the Truth value mentioned in the error.

My code:

def COSINTEGRAND(x):
    return math.cos((pi * x**2)/2)
def SININTEGRAND(x):
    return math.sin((pi * x**2)/2)
def COSINTEGRAL(u):
    return quad(COSINTEGRAND, 0, u)
def SININTEGRAL(u):
    return quad(SININTEGRAND, 0, u)

a = np.linspace(-10,10,100)
b = COSINTEGRAL(a)
print (b)

Any explanation of the error or methods to fix this would be appreciated. I got the same error when trying to plot the spiral directly- it appears to refer to a part of the scipy.integrate code

What is the dtype of the arrays here? are these numpy arrays? if so call np.cos etc — EdChum
– EdChum, Commented Mar 4, 2016 at 13:23

acdr · Accepted Answer · 2016-03-04 13:46:37Z

2

Many of the functions you're using don't know how to handle numpy arrays. This includes the scipy.integrate.quad function.

quad docs: http://docs.scipy.org/doc/scipy/reference/generated/scipy.integrate.quad.html#scipy.integrate.quad

edited Mar 4, 2016 at 13:46

answered Mar 4, 2016 at 13:24

acdr

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3 Comments

Tim Smith Over a year ago

That doesn't appear to have made a difference, unfortunately. I get an identical error when replacing math.cos and math.sin with np.cos and np.sin

acdr Over a year ago

scipy.integrate.quad's third argument (u in your COSINTEGRAL) also takes a regular float, rather than a numpy array.

Tim Smith Over a year ago

Ok, thanks. Does this mean that for me to plot the value over multiple inputs, I would have to write a loop to run the function multiple times?

ev-br · Accepted Answer · 2016-03-07 17:16:46Z

0

In this particular case, you can use Fresnel integeals as implemented in http://docs.scipy.org/doc/scipy-0.17.0/reference/generated/scipy.special.fresnel.html

answered Mar 7, 2016 at 17:16

ev-br

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