chem.js

let $ = require('meeko')

let chemSymbol =
  'H,He,Li,Be,B,C,N,O,F,Ne,Na,Mg,Al,Si,P,S,Cl,Ar,K,Ca,Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Ga,Ge,As,Se,Br,Kr,Rb,Sr,Y,Zr,Nb,Mo,Tc,Ru,Rh,Pd,Ag,Cd,In,Sn,Sb,Te,I,Xe,Cs,Ba,La,Ce,Pr,Nd,Pm,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au,Hg,Tl,Pb,Bi,Po,At,Rn,Fr,Ra,Ac,Th,Pa,U,Np,Pu,Am,Cm,Bk,Cf,Es,Fm,Md,No,Lr,Rf,Db,Sg,Bh,Hs,Mt,Ds,Rg,Cn,Nh,Fl,Mc,Lv,Ts,Og'.split(
    ','
  )
function expandElm (elm) {
  const regex = /\(([^)]+)\)(\d*)/
  return elm
    .replace(regex, (match, group, count) => {
      count = +count || 1 // default 1
      return group.repeat(count)
    })
    .replace(/\(|\)/g, '') // remove '(' ,')'
}
function chemEq2Matrix (chemStr) {
  let eqArr = chemStr.replace(/ +/g, '').split(/(\->|=|\-)/g)
  // console.log(eqArr)
  let leftEqArrOri = eqArr[0].split('+') // unexpand element
  let rightEqArrOri = eqArr[2].split('+')

  let leftEqArr = leftEqArrOri.map(x => expandElm(x))
  let rightEqArr = rightEqArrOri.map(x => expandElm(x))

  let chemElmObj = {} // element inside 有哪些元素
  eqArr = [...leftEqArr, ...rightEqArr]
  // console.log(leftEqArr, rightEqArr)
  let len = chemSymbol.length
  let leftLen = leftEqArr.length
  let rightLen = rightEqArr.length
  let matrix = [[1, ...Array(leftLen + rightLen).fill(0)]]
  for (let i = 0; i < len; i++) {
    let chemElm = chemSymbol[i]
    let rowArr = []
    let idx = 0
    for (let n = 0; n < leftLen + rightLen; n++) {
      let isElm =
        eqArr[n].match(
          new RegExp(chemElm + '[0-9]*(?=[A-Z]+|[0-9]+|$)', 'g')
        ) || [] // 同一个式子里面有多个 同样的元素
      if (isElm.length > 0) {
        let sum = $.math.sum(isElm.map(x => +x.replace(chemElm, '') || 1))
        rowArr[idx] = (idx >= leftLen ? -1 : 1) * sum
        //console.log(chemElm, sum, rowArr[idx])
        chemElmObj[chemElm] = 1
      } else {
        rowArr[idx] = 0
      }
      idx++
    }
    if (rowArr.some(x => x != 0)) {
      rowArr.push(0)
      matrix.push(rowArr)
    }
  }
  if (matrix[0].length <= matrix.length) {
    //over-determined equation 解决超定方程
    matrix.remove(0)
    for (let i = 0; i < matrix.length; i++) {
      matrix[i].remove(matrix[i].length - 1)
    }
    matrix = $.math.mat.mul($.math.mat.transpose(matrix), matrix)
    for (let i = 0; i < matrix.length; i++) {
      matrix[i].push(0)
    }
    matrix.unshift([1, ...Array(leftLen + rightLen).fill(0)]) //重新填入值
    //解决超定方程

    // 方程组大于未知数 移除有第一个主元的一行
    for (let i = 1; i < matrix.length; i++) {
      if (matrix[i][0]) {
        matrix.remove(i, 1)
        break
      }
    }
  }

  return {
    matrix,
    leftEqArr,
    rightEqArr,
    leftEqArrOri,
    rightEqArrOri,
    leftLen,
    rightLen,
    chemElmObj
  }
}

function balanceEq (chemStr) {
  try {
    // render formula
    let m = chemEq2Matrix(chemStr)
    // console.log(m)
    m.leftEqArrColor = []
    m.rightEqArrColor = []
    let pos = m.matrix[0].length - 1
    for (let i = 0; i < 200; i++) {
      let newMatrix = m.matrix.copy()
      newMatrix[0][pos] = i + 1
      let rst = $.math.gaussian(newMatrix)
      if (
        rst.every(x => {
          return $.math.approximatelyEqual(x, x.round(0) | 0)
        })
      ) {
        let newEqArr = []
        let ratio
        for (let i = 0; i < m.leftLen + m.rightLen; i++) {
          ratio = rst[i].round(0)
          if (i < m.leftLen) {
            m.leftEqArrColor[i] = $.c.y(ratio) + m.leftEqArrOri[i]
            m.leftEqArr[i] = (ratio === 1 ? '' : ratio) + m.leftEqArrOri[i]
          } else {
            m.rightEqArrColor[i - m.leftLen] =
              $.c.y(ratio) + m.rightEqArrOri[i - m.leftLen]
            m.rightEqArr[i - m.leftLen] =
              (ratio === 1 ? '' : ratio) + m.rightEqArrOri[i - m.leftLen]
          }
        }
        let outChemColorStr =
          m.leftEqArrColor.join(' + ') + ' = ' + m.rightEqArrColor.join(' + ')
        let outChemStr =
          m.leftEqArr.join(' + ') + ' = ' + m.rightEqArr.join(' + ')
        return {
          oriChem: chemStr,
          outChem: outChemStr,
          outChemCol: outChemColorStr
        }
      }
    }
    return { oriChem: chemStr, outChem: '', outChemCol: '' }
  } catch (e) {
    //TODO: 增加错误原因
    return { oriChem: chemStr, outChem: '', outChemCol: '' }
  }
}

module.exports = balanceEq