Source code in the yabasic programming language

sub perpendicularDistance(tabla(), i, ini, fin)
    local dx, cy, mag, pvx, pvy, pvdot, dsx, dsy, ax, ay

    dx = tabla(fin, 1) - tabla(ini, 1)
    dy = tabla(fin, 2) - tabla(ini, 2)
 
    //Normalise
    mag = (dx^2 + dy^2)^0.5
    if mag > 0 dx = dx / mag : dy = dy / mag
 
    pvx = tabla(i, 1) - tabla(ini, 1)
    pvy = tabla(i, 2) - tabla(ini, 2)
 
    //Get dot product (project pv onto normalized direction)
    pvdot = dx * pvx + dy * pvy
 
    //Scale line direction vector
    dsx = pvdot * dx
    dsy = pvdot * dy
 
    //Subtract this from pv
    ax = pvx - dsx
    ay = pvy - dsy
 
    return (ax^2 + ay^2)^0.5
end sub

sub DouglasPeucker(PointList(), ini, fin, epsilon)
    local dmax, index, i, d
    // Find the point with the maximum distance

    for i = ini + 1 to fin
        d = perpendicularDistance(PointList(), i, ini, fin) 
        if d > dmax index = i : dmax = d
    next

    // If max distance is greater than epsilon, recursively simplify
    if dmax > epsilon then
        PointList(index, 3) = true
        // Recursive call
        DouglasPeucker(PointList(), ini, index, epsilon)
        DouglasPeucker(PointList(), index, fin, epsilon)
    end if
end sub


data 0,0, 1,0.1,  2,-0.1,  3,5,  4,6,  5,7,  6,8.1,  7,9,  8,9,  9,9

dim matriz(10, 3)

for i = 1 to 10
    read matriz(i, 1), matriz(i, 2)
next

DouglasPeucker(matriz(), 1, 10, 1)

matriz(1, 3) = true : matriz(10, 3) = true
for i = 1 to 10
    if matriz(i, 3) print matriz(i, 1), matriz(i, 2)
next