Outside compensation curve

[jerryhenke]

Hello.

You can try this:

Code:

function linear_by_table(input,curve,offset)
local FDY = offset or 0
    fk1= (curve["y"][1] - curve["y"][2]) / (curve["x"][1] - curve["x"][2])
    fk2= (curve["y"][2] - curve["y"][3]) / (curve["x"][2] - curve["x"][3])
    fk3= (curve["y"][3] - curve["y"][4]) / (curve["x"][3] - curve["x"][4])

    if input < curve["x"][1] then
        out = curve["y"][1] + FDY;
    elseif input >= curve["x"][1] and input < curve["x"][2] then    
        out = fk1 * (input - curve["x"][1]) + curve["y"][1] + FDY
    elseif input >= curve["x"][2] and input < curve["x"][3] then
        out = fk2 * (input - curve["x"][2]) + curve["y"][2] + FDY
    elseif input >= curve["x"][3] and input < curve["x"][4] then    
        out = fk3 * (input - curve["x"][3]) + curve["y"][3] + FDY
    else
        out = curve["y"][4] + FDY
    end
 return out
end

curve = {}
curve["x"] = {-20,-10,0,20}
curve["y"] = {80,70,65,18}

--offset=2
--log(linear_by_table(20,curve,offset))
log(linear_by_table(-15,curve))

Wow. Thanks! Used this today and made some small changes.

My code looks like this and runs nicely.
 

Code:

function linear_by_table(input, curve, offset)
    local FDY = offset or 0
    local n = #curve["x"] -- Number of points
    if n ~= #curve["y"] then
        error("x and y lists must have the same number of values")
    end
    local out
    if input < curve["x"][1] then
        out = curve["y"][1] + FDY
    elseif input >= curve["x"][n] then
        out = curve["y"][n] + FDY
    else
        for i = 1, n - 1 do
            if input >= curve["x"][i] and input < curve["x"][i + 1] then
                local fk = (curve["y"][i + 1] - curve["y"][i]) / (curve["x"][i + 1] - curve["x"][i])
                out = fk * (input - curve["x"][i]) + curve["y"][i] + FDY
                break
            end
        end
    end
    return out
end
-- Define the curve for interpolation
local curve = {x = {-20, -10, 0, 10, 20}, y = {42, 34, 32, 25, 15}}
-- Adjust offset to shift the entire curve
local offset = 0
-- Get outdoor temperature from KNX address 0/3/0
local outdoor_temp = grp.getvalue('0/3/0')
-- Calculate the flow setpoint based on the outdoor temperature
local flow_setpoint = linear_by_table(outdoor_temp, curve, offset)
-- Write the calculated value to KNX address 5/5/0
grp.write('5/5/0', flow_setpoint)
-- Log the results
log('Outdoor temperature: ' .. outdoor_temp .. ', Flow setpoint: ' .. flow_setpoint)