linear_interpolation.a68

PROC lerp = ([] INT row one, [] INT row two, INT point x) INT:
BEGIN
    CO
        Linear interpolation in Algol 68
    CO

    IF ELEMS row one /= 2 OR ELEMS row two /= 2
    THEN
        stop
    FI;
    
    INT x one = row one [1];
    INT x two = row two [1];

    INT y one = row one [2];
    INT y two = row two [2];

    INT uknown y = y one + ((point x - x one)*((y two - y one) % (x two - x one)));

    uknown y

END;

BEGIN
    CO
        Y
        *
        *                    700 
        *-------------------*
        *                   |
        *      500          |
        *-----*             |
        *     |      ?      |
        *     |             |
        *     |             |
        *     |             |
        *     |             |
        **************************X
            |      |      |
            2018   2020   2024

    CO

    print(("X 1?", new line));
    INT x one = read int;

    print(("Y 1?", new line));
    INT y one = read int;

    print(("X 2?", new line));
    INT x two = read int;

    print(("Y 2?", new line));
    INT y two = read int;

    print(("X?", new line));
    INT uknown x = read int;

    [] INT row one = (x one, y one);
    [] INT row two = (x two, y two);

    INT point   = uknown x;

    INT uknown := lerp(row one, row two, point);

    print((uknown, new line))
END