Scaling values with lerp

The warmer the server room, the faster the cooling pump should run: 2 litres at 22 °C, 10 at 30 °C. Smoothly in between. That is a straight line between two points – exactly what lerp is for.

lerp#

lerp r0 a b t        # r0 = a + (b - a) * t

lerp r0 2 10 0.25 gives 4: a quarter of the way from 2 to 10.

lerp clamps the ratio#

The special thing: t is clamped to 0 to 1 first. At t = 2 the result is b, not double. At t = −1 the result is a. That saves you the clamp – the result always lies between a and b.

lerp r0 0 100 2      # 100, not 200

From reading to ratio#

You compute the ratio from the reading: (value − start) / (end − start).

sub t temp LOWER     # LOWER = 295.15, 22 C
div t t 8            # 8 degrees up to 30 C
lerp flow 2 10 t     # 2 to 10 litres

Below 22 °C t is negative, lerp turns it into 2. Above 30 °C t is greater than 1, lerp turns it into 10. That way a pump never runs below its minimum flow and never above its maximum.

Percent into device values#

A share from 0 to 1 already is a finished ratio. A battery with Ratio 0.3 converts directly: lerp r1 0 10 ratio gives 3. Percent values from 0 to 100 you divide by 100 first.

Falling curves work too: lerp flow 10 2 t gives 10 at t = 0 and 2 at t = 1 – the fuller a tank, the slower the filling pump.