philosonista - 4 months ago 21

Python Question

I'm trying to decipher some complicated code. Below, I've simplified the code, of what I do understand of it, to get to the heart of my question.

`scales = (2**arange(8, 12, .25)).astype(int)`

It seems to me that

`arange()`

But then what does

`2**arange`

`**`

Answer

Numpy arrays let you apply numeric operators to *all elements* in the array. So `array * 3`

would apply the multiplication to all elements in the array, producing a new array with the results. You can use an array on *either side* of such an expression; after all, not all operators are *commutative*.

Using `2 ** array`

simply applies each element in the array as an exponent of 2, producing an array with the `2 ** <input item>`

calculation:

```
>>> arange(8, 12, .25)
array([ 8. , 8.25, 8.5 , 8.75, 9. , 9.25, 9.5 , 9.75,
10. , 10.25, 10.5 , 10.75, 11. , 11.25, 11.5 , 11.75])
>>> 2**arange(8, 12, .25)
array([ 256. , 304.43702144, 362.03867197, 430.53896461,
512. , 608.87404288, 724.07734394, 861.07792922,
1024. , 1217.74808576, 1448.15468787, 1722.15585844,
2048. , 2435.49617153, 2896.30937574, 3444.31171688])
```

So the input is an array with `8`

, `8.25`

, `8.5`

, etc., and the resulting array contains the result of `2 ** 8`

, `2 ** 8.25`

, `2 ** 8.5`

, and so on.

The `array.astype(int)`

operation then floors the results:

```
>>> (2 ** arange(8, 12, .25)).astype(int)
array([ 256, 304, 362, 430, 512, 608, 724, 861, 1024, 1217, 1448,
1722, 2048, 2435, 2896, 3444])
```