Naismith's rule with Aitken-Langmuir corrections in Matlab, units in km and h

naismith_al.m

function [w, t, slope] = naismith_al(length, ascend, base_speed)
    if ~exist('base_speed', 'var')
        base_speed = 4; % km/h
    end
 
    slope = ascend/length;
     
    t = length*(1/base_speed);
    if slope >= 0
        t = t + ascend*(1/0.6);
    elseif atand(slope) <= -5 && atand(slope) >= -12
        t = t - abs(ascend)*((10/60)/0.3);
    elseif atand(slope) < -12
        t = t + abs(ascend)*((10/60)/0.3);
    end
     
    w = length./t;
end