R/BFfzero.R

In NLRoot: searching for the root of equation

BFfzero <-
function(f,a,b,num=10,eps=1e-5)#find the root of f(x) between [a,b]
  {
    h=abs(b-a)/num
    i=0;j=0
    a1=b1=0
    while(i<=num)
    {
      a1=a+i*h
      b1=a1+h
      if(f(a1)==0)
      {
        print(a1);print(f(a1))
      }
      else
        if(f(b1)==0)
        {
          print(b1);print(f(b1))
        }
      else
        if(f(a1)*f(b1)<0)
        {
          repeat
          {
            if(abs(b1-a1)<eps) break
            x<-(a1+b1)/2
            if(f(a1)*f(x)<0) b1<-x   else   a1<-x
          }
          print(j+1);j=j+1
          print((a1+b1)/2)
          print(f((a1+b1)/2))
        }
      i=i+1
    }
    if(j==0)print( "finding root is fail")
    else
      print("finding root is successful")
  }