Elementwise Operations
An elementwise operation applies the same operation to matching positions.
The result is:
[11 22 33]
Each element is added to the corresponding element.
Scalars apply to every element
The scalar 10 is applied to every element.
Elementwise arithmetic
Ready to run.
Elementwise multiplication is not dot product
This is elementwise:
a * b
This is a dot product:
a @ b
They answer different questions. Elementwise multiplication keeps one value per position. A dot product sums paired products into one scalar.
Predict the shape
If a.shape and b.shape are both (3,), then a + b has shape (3,).
Elementwise operations usually preserve the input shape, unless broadcasting is involved. Broadcasting comes later in this chapter.
If a = np.array([1, 2, 3]), what does a * 2 produce?
Answer it first, then check.
Hint
Apply the multiplication separately to 1, 2, and 3.
Solution
The result is:
[2 4 6]
Multiplying an array by a scalar multiplies every element by that scalar.