求助AMESim implicit variable

有谁知道 AMESim中 implicit variable 到底 是什么东东啊

   隐含变量

Implicit state variables
These have attributes which are a combination of explicit state and constraint variables (which are described in the next section). The distinctive characteristics are as follows:
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The integrator gives the submodel an estimate for both the state variable and its derivative. Submodels use these values to compute a residual. The integrator then tries to make the residual zero.
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The residual has units which can be unrelated to the units of the implicit state variable.
The state is defined by a starting value and an implicit expression for the derivative which is associated with the residual in the submodel code. An example of such an expression is given below:
This expression is used to define the residual in the submodel code:
To underline the distinction we take a second example. Imagine the one-dimensional motion of an object of mass M kg under the action of two forces f1 N and f2 N so that it moves with velocity v1 m/s. If we used an explicit state we could have the following code:
Here we explicitly define v1dot the derivative of v1. On the other hand we could use an implicit state with the following C code:

The important point is that the same variable, v1dot, is used for the derivative and the residual. On entry v1dot is an estimate (from the integrator) for the derivative of v1 and has units m/s/s. On exit it is a residual and has units N. In this case the first version is clearly better. There is only one small advantage of the second version. This is that it can tolerate (no problem) the value M=0.
Use implicit states only if there is a very good reason for doing so.

请问隐式变量和显式变量如何理解？