What does hysteresis mean and how does it apply to computer science or programming?

Question

I was looking at some code and saw an out of context comment about 'hysteresis.' I think I have figured out what the code does so my question doesn't involve anything specific. I simply do not understand what the term means or how it is applicable in programming. I looked around and saw some mathmatic definitions but would like some more information. From what I can tell Hysteresis has something to do with predicting or assuming a given state for X based on what has happened to X in the past?

Answer 1

Hysteresis characterizes a system whose behavior (output) does not only depend on its input at time t, but also on its past behavior, on the path it has followed.

A well-known device that exhibits hysteresis is a thermostat. Imagine a thermostat that would switch on and off heating at 70°F. When temperature is around 70°F, while fluctuating a bit, the thermostat would continually switch heating on and off. Generally, a thermostat is built with hysteresis: it will switch on heating at (say) 69°F, but switch off heating at 71°F. This avoids the continual switches.

EDIT: have a look at Wikipedia's article.

Answer 2

Thermostat example:

heatPointLow = 8°C
heatPointHeight = 10°C
heater = off

while(true){
    if(temperature < heatPointLow)
        heater = on
    if(temperature > heatPointHeight)   
        heater = off
}

If there where just one point the system coul'd oscillate around that single point. Between the points height and low it depends on the last value of the heater if it is on or off.