Documentation fixes

Author: birgit

windpowerlib/power_output.py

@@ -181,8 +181,9 @@ def power_curve_density_correction(wind_speed, power_curve_wind_speeds,
 
     Returns
     -------
-    list
+    pandas.Series or numpy.array
         Electrical power output of the wind turbine in W.
+        Data type depends on type of `wind_speed`.
 
     Notes
     -----

windpowerlib/tools.py

@@ -41,7 +41,7 @@ def linear_interpolation_extrapolation(df, target_height):
 
     For the inter- and extrapolation the following equation is used:
 
-    .. math:: f(x) = (f(x_2) - f(x_1)) / (x_2 - x_1) * (x - x_1) + f(x_1)
+    .. math:: f(x) = (f(x_2) - f(x_1)) / (x_2 - x_1) \cdot (x - x_1) + f(x_1)
 
     Examples
     ---------