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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?
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Hysteresis is important for producing stable switching behavior in a comparator circuit. This hysteresis is added by including a positive feedback loop between the output and one of the inputs, which then defines the threshold for switching as the input signal rises and falls.
(hɪstərisɪs) noun. (Electrical engineering: Circuits, Electrical power) Hysteresis is something that happens with magnetic materials so that, if a varying magnetizing signal is applied, the resulting magnetism that is created follows the applied signal, but with a delay.
In control systems, hysteresis can be used to filter signals so that the output reacts less rapidly than it otherwise would by taking recent system history into account.
A common example of hysteresis is the delayed effects of unemployment, whereby the unemployment rate can continue to rise even after the economy has begun recovering. The current unemployment rate is a percentage of the number of people in an economy who are looking for work but can't find any.
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.
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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.
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