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I've noticed in some French language control courses they have a word for the initial part of the response of a non-minimum phase system. They say it has "un départ malin". I looked up malin and it means different things in English, for example:

There are plenty of descriptions of the step response of such a system: the initial direction of the step response is opposite to the final value, it goes in the opposite direction to the long-term response,

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but is there a better equivalent English word to 'malin' that people commonly use to identify the non-minimum phase system response characteristic?

I've also seen the word 'undershoot' used in this context but I'm not sure that's correct.

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    \$\begingroup\$ Many words in French have technical meanings not shown in "ordinary" dictionaries and you have found one. Perhaps a "reverse start". \$\endgroup\$
    – Solar Mike
    Jul 3 '20 at 18:01
  • \$\begingroup\$ In some contexts, "kickback" might be applicable. \$\endgroup\$ Jul 3 '20 at 18:14
  • \$\begingroup\$ I don't know of a word, either. But it seems to be basically any system possessing RHPZ where actual behavior avoids it/them. \$\endgroup\$
    – jonk
    Jul 3 '20 at 18:27
  • \$\begingroup\$ it appears that the root word is mal, which means wrong ... so the phrase would be wrong start .... are you certain that the spelling is malin? \$\endgroup\$
    – jsotola
    Jul 3 '20 at 18:57
  • \$\begingroup\$ "Un départ malin", a nice way to put it but I never heard of the expression before : ) Malin has several meanings but here it means evil so it could be translated as an evil start-up if it makes sense. A non-minimum phase system could indeed include a RHP zero or a pure delay for instance. With a RHPZ, like in a boost or a buck-boost converter, if the setpoint change is too fast compared to the inductor available V-s then the output first dips before going up again. Slowing down the response - choosing a lower crossover frequency - ensures system stability. \$\endgroup\$ Jul 3 '20 at 19:57
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I think the correct term in English would be “initial inverse response”.

The system initially does the opposite of what is commanded. For example, in this book. So it’s even worse than a dead time from a control point of view.

In French, "un départ malin" seems to describe a characteristic that shows up in control of hydraulic turbines, so it is not surprising that there are a number of French-Canadian papers where it is used. @VerbalKint in an above comment connects the French and English through ‘mal’ convincingly.

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I've always heard that being called undershoot. And, in this Control Systems magazine article on Nonminimum-Phase Zeros they also call it initial undershoot.

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  • \$\begingroup\$ I'm not sure what you mean, the mathematical process itself is called an LTI system. And not only overshoot and undershoot are what you see on your oscilloscope, but they are also commonly used to describe step responses in control system, specially the maximum overshoot. But the answer from Spehro, that it is called "inverse response" also makes sense. Even though different places seem to name/reference it differently. \$\endgroup\$
    – jDAQ
    Jul 4 '20 at 2:45

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