M = zeros(400, 300);

for i = 1 : 300
    if i <= 100
        j = 2*i
    else i <= 300
        j = 0.5*i + 150
    end

    M(i, j) = 100
end

for k = 1 : 100000
    for i = 2 : 399
        if i <= 99
            j_max = 2*i
        elseif i <= 299
            j_max = 0.5*i + 150
        else
            j_max = 299
        end

        for j = 2 : j_max
            M(i, j) = 0.5*(M(i-1,j) + M(i+1,j) + M(i,j-1) + M(i,j+1))
        end
    end
end