Laba6

const killFloat = number => Number(number.toFixed(2)); // потому что в js неправильное деление и умножение
// чисел типа double

const epsilon = 0.5 * Math.pow(10, -5);

const RungeKutta3 = (xi, y, p, h, derivative) => {
    const yi = y[killFloat(xi * 10)];
    const pi = p[killFloat(xi * 10)];
    const k1 = h * pi;
    const l1 = h * (yi + 2.6 * Math.pow(xi, 3) - 2.6 * xi * xi + 5.2);
    const k2 = h * (pi + l1 / 2);
    const l2 = h * (yi + k1 / 2 + 2.6 * Math.pow(xi + h / 2, 3) - 2.6 * Math.pow(xi + h / 2, 2) + 5.2);
    const k3 = h * (pi + 2 * l2 - l1);
    const l3 = h * (yi + 2 * k2 - k1 + 2.6 * Math.pow(xi + h, 3) - 2.6 * Math.pow(xi + h, 2) + 5.2);
    const yNew = yi + (k1 + 4 * k2 + k3) / 6;
    const pNew = pi + (l1 + 4 * l2 + l3) / 6;
    const xNew = killFloat(xi + h);
    y[killFloat(xNew * 10)] = yNew;
    p[killFloat(xNew * 10)] = pNew;
    // console.info(xNew);
    // console.info('RK-3:', xNew, yNew);
    // console.info('Actual:', xNew, derivative(xNew));
    if (xNew >= 5) {
        resultt = yNew;
        return yNew;
    }
    RungeKutta3(xNew, y, p, h, derivative);
}

const thirdDerAnswer = x => Math.pow(Math.E, x) + 2 * Math.pow(Math.E, -x) - 2.6 * x * x * x + 2.6 * x * x - 15.6 * x;

const shooting = () => {
    const h = 0.2;
    const actualY = Math.pow(Math.E, 5) + 2 * Math.pow(Math.E, -5) - 338;
    let left = 0;
    let right = 5;
    let root = 0;
    const y = [];
    const x = [];
    const p = [];
    p[0] = -16.6;
    y[0] = 0;
    while (Math.abs(y[y.length - 1] - actualY) > epsilon) {
        const c = (left + right) / 2;
        y[0] = left;
        RungeKutta3(0, y, p, h, thirdDerAnswer);
        const res1 = y[y.length - 1] - actualY;
        y[0] = c;
        RungeKutta3(0, y, p, h, thirdDerAnswer)
        const res2 = y[y.length - 1] - actualY;
        root = res1 * res2;
        if (root >= 0) {
            left = c;
        } else {
            right = c;
        }
    }
    let current = 0;
    while (current <= 5) {
        // console.info('Actual:', current, thirdDerAnswer(current));
        // console.info(y[killFloat(current * 10)]);
        current = killFloat(current + h);
    }
}

const my_q = x => 2.6 * x * x * x - 2.6 * x * x + 5.2;

const myProgonka = () => {
    const h = 0.05;
    const mu = [];
    const y = [];
    const lambda = [];
    mu[0] = 16.6 * h;
    lambda[0] = 1;
    let x = h;
    for (let i = 1; i < killFloat(5 / h); i++) {
        lambda[i] = 1 / (2 + h * h - lambda[i - 1]);
        mu[i] = (my_q(x) * h * h - mu[i - 1]) / (lambda[i - 1] - 2 - h * h);
        x = killFloat(x + h);
    }
    y[lambda.length] = Math.pow(Math.E, 5) - 2 * Math.pow(Math.E, -5) - 338;
    let current = killFloat(5 - h);
    for (let i = killFloat(5 / h) - 1; i > -1; i--) {
        y[i] = lambda[i] * y[i + 1] + mu[i];
        // console.info('Computed:', y[i]);
        // console.info('Actual:', current, thirdDerAnswer(current));
        current = killFloat(current - h);
    }
    for (let num of y) {
        // console.info(num);
    }
}

myProgonka();

shooting();