Rosetta Code: Circles of given radius through two points

mlpfanatic903 · August 13, 2021, 1:07am

Tell us what’s happening:
Describe your issue in detail here.
Floating point rounding issue… Wrong floating-point data being appended to the final array. Where specifically do I need to append the statement internally in order to accommodate the final appending process…?

I would do this via

[details]
Math.floor(expr*10000)/10000;
[/details] … Could someone please help?

  **Your code so far**

const hDist = (p1,p2) => Math.hypot(...p1.map((e, i) => e-p2[i]))/2;
const pAng = (p1,p2) => Math.atan(p1.map((e,i) => e-p2[i]).reduce(
(p, c) => c/p, 1));
const solveF = (p,r) => t => [r*Math.cos(t)+p[0], r*Math.sin(t)+p[1]];
const diamPts = (p1,p2) => p1.map((e,i) => e+(p2[i]-e)/2); 
const getCircles = (...args) => {
const [p1,p2,s] = args;
const solve = solveF(p1,s), halfDist = hDist(p1,p2);
let debugMsg = `p1: ${p1}, p2: ${p2}, r:${s}`;
console.log(`${debugMsg}`);
let msg = `Result: `, dCheck = Math.sign(s-halfDist), newArr = [];
switch (dCheck) {
  case 0:
    s ? newArr.push(diamPts(p1,p2)) : (msg='Radius Zero');
    break;
  case 1:
    if (!halfDist) {
      msg = 'Coincident point. Infinite solutions';
    } else {
      let theta = pAng(p1,p2), theta2 = Math.acos(halfDist/s);
      [1,-1].map(e => solve(theta + e*theta2)).forEach(e => 
      newArr.push(e));
    }
    break;
  case -1:
    msg ='No intersection. Points further apart than circle diameter';
    break;
} 
  console.log(`BEFORE: newArr: ${newArr}`);
  newArr.forEach((el) => el = [Math.floor(el[0]*10000)/10000, 
    Math.floor(el[1]*10000)/10000]);
  console.log(`AFTER: newArr: ${newArr}`);
  return (msg !=`Result: `) ? (msg): newArr; 
};

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 Safari/537.36

Challenge: Circles of given radius through two points

Link to the challenge:

sanity · August 13, 2021, 4:31am

forEach doesn’t mutate array on it own and it always returns undefined, callback function might mutate the array, but it’d be more complicated than this. Consider using map method instead.

mlpfanatic903 · August 13, 2021, 8:52pm

Got the map for nA1, new map that floats corresponding… It’s flipping me the bird by making the second mapped el to be off by (+/- 1.0e-4)…
Else, it worked perfectly… Thank you for the assist.

const hDist = (p1,p2) => Math.hypot(...p1.map((e, i) => e-p2[i]))/2;
const pAng = (p1,p2) => Math.atan(p1.map((e,i) => e-p2[i]).reduce(
(p, c) => c/p, 1));
const solveF = (p,r) => t => [r*Math.cos(t)+p[0], r*Math.sin(t)+p[1]];
const diamPts = (p1,p2) => p1.map((e,i) => e+(p2[i]-e)/2); 
const getCircles = (...args) => {
  const [p1,p2,s] = args;
  const solve = solveF(p1,s), halfDist = hDist(p1,p2);
  let debugMsg = `p1: ${p1}, p2: ${p2}, r:${s}`;
  console.log(`${debugMsg}`);
  let msg = `Result: `, dCheck = Math.sign(s-halfDist), newArr = [];
  if (dCheck == 0){
      s ? newArr.push(diamPts(p1,p2)) : (msg='Radius Zero');
     } else if (dCheck ==1) {
       if (!halfDist) {
        msg = 'Coincident point. Infinite solutions';
      } else {
        let theta = pAng(p1,p2), theta2 = Math.acos(halfDist/s);
        [1,-1].map(e => solve(theta + e*theta2)).forEach(e => 
        newArr.push(e));
      } } else if(dCheck == -1) {
      msg ='No intersection. Points further apart than circle diameter';
      }
    let nA1 = newArr.map((el) => el = [(Math.floor(el[0]* 10000)/10000).toFixed(4),(Math.floor(el[1]*10000)/10000).toFixed(4)]);
    let consoleStrDebug = `nA1:`;
    if(nA1.length > 1) {consoleStrDebug += '['; }
    for(let i=0; i < nA1.length; i++) {
      let finalChar = (i < nA1.length-1) ? ', ':'';
     consoleStrDebug +=`[${nA1[i][0]},${nA1[i][1]}]${finalChar}`;
    }
    if(nA1.length > 1) {consoleStrDebug += ']'; }
    console.log(`${consoleStrDebug}\n`);
    return (msg !=`Result: `) ? (msg): nA1; 
};

sanity · August 14, 2021, 4:42am

Take a closer look at the calculations rounding the coordinates. To be a little more specific consider what actually happens when Math.floor method is used on the number below a zero.

mlpfanatic903 · August 14, 2021, 1:44pm

In other words,

(round(expr*10000)/10000).toFixed(4)

in order to allow for upwards/ downwards modification…

sanity · August 14, 2021, 3:07pm

Yes. There’s left just one small detail with using toFixed. It returns string and number of decimals is always the number passed to it, even if that would be only 0s. So it is here not needed.

mlpfanatic903 · August 14, 2021, 6:44pm

const hDist = (p1,p2) => Math.hypot(...p1.map((e, i) => e-p2[i]))/2;
const pAng = (p1,p2) => Math.atan(p1.map((e,i) => e-p2[i]).reduce(
(p, c) => c/p, 1));
const solveF = (p,r) => t => [r*Math.cos(t)+p[0], r*Math.sin(t)+p[1]];
const diamPts = (p1,p2) => p1.map((e,i) => e+(p2[i]-e)/2); 
const getCircles = (...args) => {
  const [p1,p2,s] = args;
  const solve = solveF(p1,s), halfDist = hDist(p1,p2);
  let debugMsg = `p1: ${p1}, p2: ${p2}, r:${s}`;
  console.log(`${debugMsg}`);
  let msg = `Result: `, dCheck = Math.sign(s-halfDist), newArr = [];
  if (dCheck == 0){
      s ? newArr.push(diamPts(p1,p2)) : (msg='Radius Zero');
     } else if (dCheck ==1) {
       if (!halfDist) {
        msg = 'Coincident point. Infinite solutions';
      } else {
        let theta = pAng(p1,p2), theta2 = Math.acos(halfDist/s);
        [1,-1].map(e => solve(theta + e*theta2)).forEach(e => 
        newArr.push(e));
      } } else if(dCheck == -1) {
      msg ='No intersection. Points further apart than circle diameter';
      }
    let nA1 = newArr.map((el) => el = [(Math.round(el[0]*10000)/10000),
    (Math.round(el[1]*10000)/10000)]);
    let consoleStrDebug = `nA1:`;
    if(nA1.length > 1) { consoleStrDebug += '['; }
    for(let i=0; i < nA1.length; i++) {
      let finalChar = (i < nA1.length-1) ? ', ':'';
     consoleStrDebug +=`[${nA1[i][0]},${nA1[i][1]}]${finalChar}`;
    }
    if(nA1.length > 1) {consoleStrDebug += ']'; }
    console.log(`${consoleStrDebug}\n`);
    return (msg !=`Result: `) ? (msg): nA1; 
};

// running tests

getCircles([0.0000, 2.0000], [0.0000, 0.0000], 1.0)

should return

[0, 1]

// tests completed 
// console output 
p1: 0.1234,0.9876, p2: 0.8765,0.2345, r:2 
nA1:[[1.8631,1.9742], [-0.8632,-0.7521]] 

p1: 0,2, p2: 0,0, r:1 
nA1:[0,1] 

p1: 0.1234,0.9876, p2: 0.1234,0.9876, r:2 
nA1: p1: 0.1234,0.9876, p2: 0.8765,0.2345, r:0.5

nA1: 

p1: 0.1234,0.9876, p2: 0.1234,0.9876, r:0 
nA1:

… Needless to say, it is really close, just something is going wrong…

sanity · August 14, 2021, 7:11pm

Printing to console the actual return value should give some idea what’s wrong:

console.log(getCircles([0.0000, 2.0000], [0.0000, 0.0000], 1.0))

mlpfanatic903 · August 14, 2021, 7:15pm

It’s a multi-dim array… Bollocks…

mlpfanatic903 · August 14, 2021, 10:37pm

const hDist = (p1,p2) => Math.hypot(...p1.map((e, i) => e-p2[i]))/2;
const pAng = (p1,p2) => Math.atan(p1.map((e,i) => e-p2[i]).reduce(
(p, c) => c/p, 1));
const solveF = (p,r) => t => [r*Math.cos(t)+p[0], r*Math.sin(t)+p[1]];
const diamPts = (p1,p2) => p1.map((e,i) => e+(p2[i]-e)/2); 
const getCircles = (...args) => {
  const [p1,p2,s] = args;
  const solve = solveF(p1,s), halfDist = hDist(p1,p2);
  let debugMsg = `p1: ${p1}, p2: ${p2}, r:${s}`;
  console.log(`${debugMsg}`);
  let msg = `Result: `, dCheck = Math.sign(s-halfDist), newArr = [];
  if (dCheck == 0){
      s ? newArr.push(diamPts(p1,p2)) : (msg='Radius Zero');
     } else if (dCheck ==1) {
       if (!halfDist) {
        msg = 'Coincident point. Infinite solutions';
      } else {
        let theta = pAng(p1,p2), theta2 = Math.acos(halfDist/s);
        [1,-1].map(e => solve(theta + e*theta2)).forEach(e => 
        newArr.push(e));
      } } else if(dCheck == -1) {
      msg ='No intersection. Points further apart than circle diameter';
      }
    let nA1 = [];
    for(let i=0; i< newArr.length; i++){
      if(newArr.length == 1) { 
        nA1 = [(Math.round(newArr[i][0]*10000)/10000),
                (Math.round(newArr[i][1]*10000)/10000)]; 
      } else {
        nA1.push([(Math.round(newArr[i][0]*10000)/10000),
                (Math.round(newArr[i][1]*10000)/10000)]);
      } 
    }  
    let consoleStrDebug = `nA1:`;
    if(nA1.length > 1) { consoleStrDebug += '['; }
    for(let i=0; i < nA1.length; i++) {
      let finalChar = (i < nA1.length-1) ? ', ':'';
     consoleStrDebug +=`[${nA1[i][0]},${nA1[i][1]}]${finalChar}`;
    }
    if(nA1.length > 1) {consoleStrDebug += ']'; }
    console.log(`${consoleStrDebug}\n`);
    return (msg !=`Result: `) ? (msg): nA1; 
};

system · February 13, 2022, 10:37am

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