---
title: geometricProgression
tags: math,algorithm,intermediate
---

Initializes an array containing the numbers in the specified range where `start` and `end` are inclusive and the ratio between two terms is `step`.
Returns an error if `step` equals `1`.

- Use `Array.from()`, `Math.log()` and `Math.floor()` to create an array of the desired length, `Array.prototype.map()` to fill with the desired values in a range.
- Omit the second argument, `start`, to use a default value of `1`.
- Omit the third argument, `step`, to use a default value of `2`.

```js
const geometricProgression = (end, start = 1, step = 2) =>
  Array.from({
    length: Math.floor(Math.log(end / start) / Math.log(step)) + 1,
  }).map((_, i) => start * step ** i);
```

```js
geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]
geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]
geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]
```