解方程 （允许误差）

1. 确定范围
2. 确定误差
3. 确定增量
4. 在区间内执行方程，满足误差存入解集
5. 返回解集

var solveFun = function(
f /*function*/,
c /*closest to 0*/,
from /*from what number*/,
to /*to what number*/,
ic /*increasement*/){

var arr = new Array();
for(var i =from ; i <= to ; i+=ic){
var r = f(i);
if(Math.abs(r) <= c) {arr.push({x:i,y:r});}
}

if(arr.length == 0) {return undefined;}

return arr;
}

var ret = solveFun(function (n){return n*n*n -3*n + 1},0.001,-10,20,0.001);

if(ret == undefined){console.log("no answer.");}

else {
console.log(ret.length + "answer found ");
for(var i = 0 ;i < ret.length; i++)
console.log("x = " + ret[i].x + ", y= " + ret[i].y);

}

解方程 （允许误差）