Rethink Computing

Category: Uncategorized

  • Why Predicting the Next Day Price of a Stock Using the Stock’s Price History Is Impossible, with a DNN.

    It can always be a fascinating dream to predict the next day price of a stock by looking at the stock’s price curve. However, by thinking it through, I doubt the meaningfulness of do so, even with a very powerful technology, deep neural network.

    A stock’s price, as time goes, rises or falls, from minute to minute. To view it abstractly, one can think of it can a continuous curve. A prediction task usually shifts a time window from past time toward current time. In each shift of the window, the oldest value is removed, and a newest value is added. In this process, one problem happens, that is the subsequence of any window is very similar to the subsequence of the next window. And next day’s price can either rise or fall, seemingly randomly. So, the input dataset is like assigning different labels to the same input data. Hence, the best that any model can do it to make a random guess on whether the next day’s price will rise or fall.

    Some people have made some videos on predicting stock price using LSTM, or other models. As long as they use the stock price history to predict price of the same stock, it will not work, just because the inputs do not distinguish labels.

    However, does it mean that stock prices cannot be predicted? Asserting this is still too early. There can be some relationships among various stocks, so there is still some possibility that one stock’s price can be predicted by other stocks.

  • Rust練習問題：弟の算数検査

    問題文

    弟は100以内の足し算と引き算をやりました。チャックしてあげてください。核問題の形式はa+b=c或いはa-b=c、どれも100を超えない非負整数です。cは弟が算出した回答で、200以内の比数整数であるか、一個の「?」かです。「?」は回答不能を意味します。

    入力形式

    入力は100行以内とし、EOF記号で終了します。一行ごとに、一問があります。形式は前述規定に則し、いかなるスペースを含みません。入力されたすべての整数に左に不要な0をつけていません。

    出力形式

    一行のみを出力します。一個の非負整数のみが出て、つまり、弟が正解した問題の数。

    入力サンプル

    1+2=3
    3-1=5
    6+7=?
    99-0=99

    回答案

    use std::io;
use core::iter::Peekable;
use core::str::Chars;
pub struct Expression {
    a: i32,
    b: i32,
    op: char,
    answer: i32,
    unanswered: bool
}

fn main() {
    let mut line: String = String::new();
    let mut correct_count: i32 = 0;
    while io::stdin().read_line(&mut line).unwrap() > 0 {
        let mut char_seq: Peekable<Chars<'_>> = line.trim().chars().peekable();
        let a: i32   = read_number(&mut char_seq).unwrap().unwrap();
        let op: char = char_seq.next().unwrap();
        let b: i32   = read_number(&mut char_seq).unwrap().unwrap();
        assert!(char_seq.next().unwrap()=='=');
        let got_answer = read_number(&mut char_seq).unwrap();
        let expression = Expression {
            a: a,
            op: op,
            b: b,
            answer: got_answer.unwrap_or_default(),
            unanswered: got_answer.is_none()
        };
        match check_expression(&expression) {
            Ok(r) => correct_count += if r {1} else {0},
            Err(e) => println!("Error: {}", e)
        }
        line.clear();
    }
    println!("{}", correct_count);
}

fn read_number(text_iter: &mut Peekable<Chars<'_>>) -> Result<Option<i32>, &'static str> {
    let mut number_str: String = String::new();
    while let Some(&c) = text_iter.peek() {
        match c {
            c if c >= '0' && c <= '9' => {
                number_str.push(c);
                text_iter.next();
            },
            '?' => {
                number_str.push(c);
                text_iter.next();
                break;
            },
            _ => break
        }
    }
    if number_str == "?" {
        Ok(None)
    } else if number_str.len() > 0 {
        Ok(Some(number_str.parse().unwrap()))
    }
    else {
        Err("Reading a number while not at a number.")
    }
}

fn check_expression(expr: &Expression) -> Result<bool, &'static str> {
    let expected: i32;
    match expr.op {
        '+' => expected = expr.a + expr.b,
        '-' => expected = expr.a - expr.b,
        '*' => expected = expr.a * expr.b,
        '/' => expected = expr.a / expr.b,
        _ => return Err("Invalid operator.")
    }
    Ok(!expr.unanswered && expr.answer == expected)
}

  • Start Anew

    It has been a year perhaps? I lost my sites. Now it’s about time to start anew.

    With this simple post, I just try to get familiar with the newest WordPress functions at the time of being.