metoda.secen <- function(f, x01, x02, tol=1e-5, maxit=20){
  x1<- x01
  x2 <- x02
  body <- c(x1,x2)
  for (iter in 1:maxit){
    df <- (x2-x1)/(f(x2)-f(x1))*f(x2)
    x <- x2-df
    body <- c(body, x)
    x1 <- x2
    x2 <- x
    if      (f(x)==0) {return(result <- list(koren=x, pocitadlo=iter+2, chyba=0, body=body))}
    else if (abs(df) < tol){
      result <- list(koren=x, pocitadlo=iter, chyba=(x2-x1)/(f(x2)-f(x1))*f(x2), 
                     body=body)
      return(result)  
    }
  }
}