javascript - Rotating 2D Vector by unknown angle such that its direction vector is [1,0] -


i trying rotate vector [x,y] around origin such when rotation completed lies on x axis. in order this, i'm first computing angle between [x,y] , [1,0], applying simple 2d rotation matrix it. i'm using numericjs work vectors.

math.anglebetween = function(a, b) {                                                                                                    var x = numeric.dot(a, b) / (numeric.norm2(a) * numeric.norm2(b));                                                                  if(math.abs(x) <= 1) {                                                                                                                  return math.acos(x);                                                                                                            } else {                                                                                                                                throw "bad input anglebetween";                                                                                              }                                                                                                                               };  math.aligntox = function(v) {     var theta = -math.anglebetween([1,0], v);     var r = [[math.cos(theta), -math.sin(theta)],              [math.sin(theta), math.cos(theta)]];     return numeric.dot(r, v); };

(note: math namespace object within project. math ye olde math object.)

this code works sometimes, there occasions no matter how many times run math.aligntox vector never gets close aligning x axis. i'm testing checking if y coordinate less 1e-10.

i've tried using math.atan2 implicit z coordinate of 0, results have been same. errors not being thrown. example results:

math.aligntox([152.44444444444434, -55.1111111111111])  // result: [124.62691466033475, -103.65652585400568] // expected: [?, 0]  math.aligntox([372, 40]) // result: [374.14435716712336, -2.0605739337042905e-13] // expected: [?, 0] // value has abs(y coordinate) < 1e-10, considered aligned

what doing wrong?

if you're rotating other vector, you'll need use r matrix. if need rotate vector, result [math.sqrt(x*x+y*y),0].


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