I didn't understand the yellow-marked sentence clearly, and even I did, what does it have to do with the conclusion that follows it? (marked in green). Thanks in advance..

Source: Modern control engineering 5th ed, chapter 2, state-space, page 30

**Modern control engineering 5th ed, chapter 2, state-space, page 30**

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    \$\begingroup\$ What is the source for this document and on what page is the quote. Context is needed. \$\endgroup\$ – Andy aka Dec 4 '18 at 12:20
  • \$\begingroup\$ It is a value that you use to compare against when making PID calculations for instance. The other terms are current as at this instant and have no history component. \$\endgroup\$ – KalleMP Dec 4 '18 at 12:50
  • \$\begingroup\$ @Andy aka It's contained in the post now.. \$\endgroup\$ – Yuri Dec 4 '18 at 13:27
  • \$\begingroup\$ @KalleMP, thank you my friend, but how to use them as memory devices? \$\endgroup\$ – Yuri Dec 4 '18 at 13:28

An integrator has its current state (value) because of the past values.

That is kind of a memory: It memorizes the sum of the "past".

The green sentence follows from the yellow sentence because the yellow sentence defines the integrators as state, and the green sentence just repeats that.

  • \$\begingroup\$ Oh, I see, thanks a lot. But why does the number of state variables equal the number of integrator outputs here ? \$\endgroup\$ – Yuri Dec 4 '18 at 13:29
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    \$\begingroup\$ because ... yellow sentence. \$\endgroup\$ – Marcus Müller Dec 4 '18 at 13:31

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