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javascript/snippets/geometric-progression.md

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+---
+title: Geometric progression
+type: snippet
+tags: [math,algorithm]
+cover: book-chair
+excerpt: Initializes an array containing the numbers in the specified geometric progression range.
+dateModified: 2020-12-28T13:49:24+02:00
+---
+
+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]
+```