How do I vecture this calculation in numpy

Nothing, there is a trick ufunc

that works if you are doing any algebra. In this case, it ufunc

is multiply

a trick accumulate

.

c = np.r_[np.multiply.accumulate(b[0:-1][::-1])[::-1], 1]
total2 = np.sum(a * c)

      

        
        
        
      

    

What it is: Algebraically, you sum a[i]

multiply times b[i:]

by for i in range(a.size)

. To do this, turn over b

and get the launched product of everything but the last number (assuming a

both b

are the same length), and then put it back. The last value should be 1 because the final value is a

just added.

Testing

a = np.random.randint(1, 10, 40)
b = 1 + np.random.rand(40)

total = a[0]
for ix in range(1, len(a)):
   total = total*b[ix-1] + a[ix]

total
278443993.10494208

total2
278443993.10494208