nsolvejs/lib/linearinterpolation.js

Solve equations using numerical methods

module.exports = function (arraytointerpolate) {
  arraytointerpolate = arraytointerpolate || [];
  const _arraytosearch = [];
  let length;

  /** @prop array interpoleted. */
  this.arraytointerpolate = arraytointerpolate;
  length = this.arraytointerpolate.length - 1;
  for (let i = 0; i <= length; i++) _arraytosearch[i] = arraytointerpolate[i][0];

  this.arraytosearch_x = _arraytosearch;

  /** @method Define the function interpolated. */
  this.function_interpolated = function (x) {
    const a = _arraytosearch[0];
    const beta = _arraytosearch[length];
    const N = length;
    let A = {};
    let B = {};
    let m; let b; let
      n;
    if (x < a || x > b || !x || !a || !beta) return;

    // Here is supposed that points distribution is linear.
    n = Math.floor((x - a) / (beta - a) * (N - 1));
    if (n < 0 || n > N - 1 || !arraytointerpolate[n]) return;

    A = {
      x: arraytointerpolate[n][0],
      y: arraytointerpolate[n][1],
    };
    B = {
      x: arraytointerpolate[n + 1][0],
      y: arraytointerpolate[n + 1][1],
    };
    m = (B.y - A.y) / (B.x - A.x);
    b = A.y - A.x * m;
    return m * x + b;
  };
};