ESP8266 Community Forum

- Fri Sep 08, 2017 1:08 am #69802 I didn't use the c source, but I coded some functions directly in lua. It may help you.

I had a need for math.sin(), math.cos(), math.atan() and math.atan2() which are omitted from the lua builds. Here are the versions I finally used. They may be useful to others. I used them for accelerator pitch and roll, and for GPS distance and bearing.

Code: Select allfunction math_atan (X0)
    -- https://stackoverflow.com/questions/11930594/calculate-atan2-without-std-functions-or-c99
    -- excellect formula for 0 - 45degr [ie atan(x) for x<1] but runs away badly for x very large
    -- but we can cheat using symmetry of atan(x) and atan(1/x) around 45degr (0 - 45 - 90)
    local X = X0
    local c = (1 + math.sqrt(17)) / 8
    if X0 < 0 then X = -X0 end
    if X0 > 1  then X = 1/X end
    local A =  (c * X + X*X + math.pow(X,3)) / ( 1 + (c + 1) * X + (c + 1) * X*X + math.pow(X,3)) * math.pi/2
    if X0 > 1  then A = math.pi/2 -A end
    if X0 < 0 then A = -A end
    return A
    -- in radian
end

function math_atan2(AW,AZ)
    local A = math_atan(AW/AZ)
    -- https://en.wikipedia.org/wiki/Atan2#Definition
    if AZ>0 then return A end
    if AZ<0 then
        if AW>=0 then return A + math.pi end
        return A - math.pi
    end
    if AW>0 then return math.pi / 2 end
    if AW<0 then return (-math.pi/2) end
    return 0 -- undef??
    -- in radian
end

local function factl(n)
    if n==1 then return 1 end
    return n * factl(n-1)
end

function math_sin(x)
    -- taylor series. Exc accuracy -PI to +PI.  Ref  https://en.wikipedia.org/wiki/Taylor_series
    -- x in radian
    x=(x%(2*math.pi)-math.pi)
    local ss=x
    - math.pow(x,3)/factl(3)
    + math.pow(x,5)/factl(5)
    - math.pow(x,7)/factl(7)
    + math.pow(x,9)/factl(9)
    - math.pow(x,11)/factl(11)
    return(-ss)  -- minus because we slid graph left by PI
end

function math_cos(x)
    return math.sqrt(1-math.pow(math_sin(x),2))  -- sin^2 + cos^2 = 1
end


Actually, I made them work as math.sin(x) etc like the inbuilt math functions, as per the cloning/overloading method used here:

https://github.com/BLavery/esuite-lua/b ... b-MATH.lua

Hope this may help.