.sum()

The `.sum()` function sums the elements of an array over a given axis.

Syntax

``numpy.sum(a, axis, dtype, out, keepdims, initial, where)``

The `a` argument is required and represents the array of elements to sum. All other arguments are optional. Used by itself, `a` will result in a scalar that sums all the elements of the array.

`.sum()` provides the following arguments:

• `a`: The array of elements to sum.
• `axis`: An int or tuple of ints specifying the axis/axes along which to sum.
• `dtype`: The type of the returned array and the accumulator used to sum elements. Defaults to the dtype of `array`.
• `out`: An `ndarray` to receive result. Must have the same shape as expected output.
• `keepdims`: A boolean if true will keep reduced axes in the result as dimensions with size one.
• `inital`: The starting value for sum.
• `where`: A boolean array that maps to `array` and selects elements to include into the sum.

Example

The following example creates an array then uses a few `.sum()` operations to sum the elements.

```import numpy as np
nd = np.array([[1,2,3],[4,5,6]])
print(np.sum(nd))print(np.sum(nd, axis=0))print(np.sum(nd, axis=1))```

This produces the following output:

`21[5 7 9][ 6 15]`

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