Numpy how to vectorize python function use np.cumprod

Question

I have a python function:

pval = np.array([1,1,1,1,1,0.999709, 0.99973,0.999743,0.999706, 0.999675, 0.99965,  0.999629])
age1=4
age2=8

def getnpxtocert(mt, age, age2):
    val = mt[age]
    for i in range(age + 1,age2):
        val = val * mt[i]
    return val

getnpxtocertv(pval,age1,age2)

The output is:

0.9991822227268075

And then I tried to use cumprod to vectorize it:

def getnpxtocertv(mt, age, age2):
    return (mt[age]*np.cumprod(mt[age+1:age2])).sum()

getnpxtocert(pval,age1,age2)

But the output is:

2.998330301296807

What did I wrong?Any friend can help?

Warren Weckesser · Accepted Answer · 2021-10-06 02:12:37Z

2

You don't need cumprod and sum. Just use prod:

def getnpxtocert_v2(mt, age, age2):
    return np.prod(mt[age:age2])

Comparison:

In [23]: getnpxtocert(pval, age1, age2)
Out[23]: 0.9991822227268075

In [24]: getnpxtocert_v2(pval, age1, age2)
Out[24]: 0.9991822227268075

cumprod takes an array [x0, x1, x2, ...] and returns an array with the same length containing [x0, x0*x1, x0*x1*x2, ...]. prod returns the scalar that is the product of all the elements x0*x1*x2*....

edited Oct 6, 2021 at 2:12

answered Oct 6, 2021 at 2:07

Warren Weckesser

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2 Comments

William Over a year ago

Thank you for your right answer,it works,can you also help this one stackoverflow.com/questions/69457867/…

William Over a year ago

Hi friend can you help me with this one ? stackoverflow.com/questions/69484626/…

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