30 lines
1.1 KiB
Markdown
30 lines
1.1 KiB
Markdown
---
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title: Geometric progression
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tags: math,algorithm
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expertise: intermediate
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cover: blog_images/book-chair.jpg
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excerpt: Initializes an array containing the numbers in the specified geometric progression range.
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firstSeen: 2018-01-03T09:36:23+02:00
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lastUpdated: 2020-12-28T13:49:24+02:00
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---
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Initializes an array containing the numbers in the specified range where `start` and `end` are inclusive and the ratio between two terms is `step`.
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Returns an error if `step` equals `1`.
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- 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.
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- Omit the second argument, `start`, to use a default value of `1`.
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- Omit the third argument, `step`, to use a default value of `2`.
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```js
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const geometricProgression = (end, start = 1, step = 2) =>
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Array.from({
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length: Math.floor(Math.log(end / start) / Math.log(step)) + 1,
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}).map((_, i) => start * step ** i);
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```
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```js
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geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]
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geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]
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geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]
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```
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