Washington Post | Ezra Klein | An ugly word for an ugly economyI just learned that economists have a slightly different definition of "hysteresis" than the one I am familiar with, which is similar but not very precisely described simply by "a lagging effect."
You may not know the term 'hysteresis.' It's the 'lagging of an effect behind its cause,' and it's an ugly word that sounds like a foot fungus. It's also an ugly thing to have happen to your economy. And it may be what's happening to ours."
I have heard the word used, typically when discussing complex systems research, to refer to a system in which the current output is not defined by the current input, but by a combination of the current input and the previous state or previous output.
The common explanation involves a thermostat. We go now to Wikipedia for the example:
A system may be explicitly designed to exhibit hysteresis, especially in control theory. For example, consider a thermostat that controls a furnace. The furnace is either off or on, with nothing in between. The thermostat is a system; the input is the temperature, and the output is the furnace state. If one wishes to maintain a temperature of 20 °C, then one might set the thermostat to turn the furnace on when the temperature drops below 18 °C, and turn it off when the temperature exceeds 22 °C. This thermostat has hysteresis. If the temperature is 21 °C, then it is not possible to predict whether the furnace is on or off without knowing the history of the temperature.
LOL! I had a similar reaction when I read that quote. "WTF, that's not what hysteresis means!"
ReplyDeleteAs a mechanical engineer, you run into hysteresis error in measurement systems and in automated systems.
Many physical and electronic measurement systems have some slight hysteresis error wherein the measurement of the same exact thing will differ slightly based on whether one approaches the measurement from a higher value or a lower value.
Similarly, if one tells a robot conveyor to move the brick to point B on a line, it will be a slightly different position based on whether the brick started at point A(less than)B or point C(greater than)B.
PS - I hate that the use of html in comments prevents me from using less-than and greater-than symbols for their intended purposes.