29 lines
969 B
Markdown
29 lines
969 B
Markdown
---
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title: vectorAngle
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tags: math, beginner
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---
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Returns the angle (theta) value between two vectors.
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Use `Math.trunc()` to convert the half of `length` to integer.
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Use `Array.prototype.slice()` slice the incoming array into two vectors.
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Use `Array.prototype.reduce()`, `Math.pow()` and `Math.sqrt()` to calculate the magnitude of each vector and the scalar product of the two vectors.
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Use `Math.acos()` to calculate arccos and get the theta.
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```js
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const vectorAngle = (...x) =>{
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let half = Math.trunc(x.length / 2);
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let [a, b] = [x.slice(0, half), x.slice(half)];
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let magnitudeOfA = Math.sqrt(a.reduce((total, num) => {return total + Math.pow(num, 2);}, 0));
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let magnitudeOfB = Math.sqrt(b.reduce((total, num) => {return total + Math.pow(num, 2);}, 0));
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let scalar = a.reduce((total, num, i)=>{return total + (num * b[i])}, 0);
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return Math.acos(scalar / (magnitudeOfA * magnitudeOfB));
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};
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```
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```js
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vectorAngle(3,4,4,3); // 0.283794109208328
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```
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