Merge pull request #83 from JuliaControl/doc_correction

doc: change nomenclature EMPC

Author: franckgaga

docs/src/manual/nonlinmpc.md

@@ -153,17 +153,17 @@ See [`sim!`](@ref) documentation for details on the possible simulation scenario
 ## Economic Model Predictive Controller
 
 Economic MPC can achieve the same objective but with lower economical costs. For this case
-study, the controller will aim to reduce the energy consumed by the motor. The power (W)
+study, the controller will aim to reduce the energy consumed by the motor. The power in watt
 transmitted by the motor to the pendulum is:
 
 ```math
-Ẇ(t) = τ(t) ω(t)
+P(t) = τ(t) ω(t)
 ```
 
-Thus, the work (J) done by the motor from ``t = t_0`` to ``t_{end}`` is:
+Thus, the work in joule done by the motor from ``t = t_0`` to ``t_{end}`` is:
 
 ```math
-W = \int_{t_0}^{t_{end}} Ẇ(t) \mathrm{d}t = \int_{t_0}^{t_{end}} τ(t) ω(t) \mathrm{d}t
+W = \int_{t_0}^{t_{end}} P(t) \mathrm{d}t = \int_{t_0}^{t_{end}} τ(t) ω(t) \mathrm{d}t
 ```
 
 With the sampling time ``T_s`` in s, the prediction horizon ``H_p``, the limits defined as