NumPy Summations
Summations
What is the difference between summation and addition?
Addition is done between two arguments whereas summation happens over n elements.
Example
Add the values in arr1 to the values in arr2:
import numpy as np
arr1 = np.array([1, 2, 3])
arr2 = np.array([1, 2,
3])
newarr = np.add(arr1, arr2)
print(newarr)
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Returns: [2 4 6]
Example
Sum the values in arr1 and the values in arr2:
import numpy as np
arr1 = np.array([1, 2, 3])
arr2 = np.array([1, 2,
3])
newarr = np.sum([arr1, arr2])
print(newarr)
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Returns: 12
Summation Over an Axis
If you specify axis=1, NumPy will sum the
numbers in each array.
Example
Perform summation in the following array over 1st axis:
import numpy as np
arr1 = np.array([1, 2, 3])
arr2 = np.array([1, 2,
3])
newarr = np.sum([arr1, arr2], axis=1)
print(newarr)
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Returns: [6 6]
Cummulative Sum
Cummulative sum means partially adding the elements in array.
E.g. The partial sum of [1, 2, 3, 4] would be [1, 1+2, 1+2+3, 1+2+3+4] = [1, 3, 6, 10].
Perfom partial sum with the cumsum() function.
Example
Perform cummulative summation in the following array:
import numpy as np
arr = np.array([1, 2, 3])
newarr = np.cumsum(arr)
print(newarr)
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Returns: [1 3 6]
