Add atand function (#1927)

* Add atand function

* Fix

* Fix me again

* Last fix promise

* Update pvlib/tools.py

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

* Apply suggestions from code review

Thanks for these improvements @adriesse

Co-authored-by: Anton Driesse <anton.driesse@pvperformancelabs.com>

---------

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>
Co-authored-by: Anton Driesse <anton.driesse@pvperformancelabs.com>

Author: 3 people

pvlib/tools.py

@@ -11,7 +11,7 @@
 
 def cosd(angle):
     """
-    Cosine with angle input in degrees
+    Trigonometric cosine with angle input in degrees.
 
     Parameters
     ----------
@@ -23,14 +23,13 @@ def cosd(angle):
     result : float or array-like
         Cosine of the angle
     """
-
     res = np.cos(np.radians(angle))
     return res
 
 
 def sind(angle):
     """
-    Sine with angle input in degrees
+    Trigonometric sine with angle input in degrees.
 
     Parameters
     ----------
@@ -42,14 +41,13 @@ def sind(angle):
     result : float
         Sin of the angle
     """
-
     res = np.sin(np.radians(angle))
     return res
 
 
 def tand(angle):
     """
-    Tan with angle input in degrees
+    Trigonometric tangent with angle input in degrees.
 
     Parameters
     ----------
@@ -61,14 +59,13 @@ def tand(angle):
     result : float
         Tan of the angle
     """
-
     res = np.tan(np.radians(angle))
     return res
 
 
 def asind(number):
     """
-    Inverse Sine returning an angle in degrees
+    Trigonometric inverse sine returning an angle in degrees.
 
     Parameters
     ----------
@@ -80,14 +77,13 @@ def asind(number):
     result : float
         arcsin result
     """
-
     res = np.degrees(np.arcsin(number))
     return res
 
 
 def acosd(number):
     """
-    Inverse Cosine returning an angle in degrees
+    Trigonometric inverse cosine returning an angle in degrees.
 
     Parameters
     ----------
@@ -99,11 +95,28 @@ def acosd(number):
     result : float
         arccos result
     """
-
     res = np.degrees(np.arccos(number))
     return res
 
 
+def atand(number):
+    """
+    Trigonometric inverse tangent returning an angle in degrees.
+
+    Parameters
+    ----------
+    number : float
+        Input number
+
+    Returns
+    -------
+    result : float
+        arctan result
+    """
+    res = np.degrees(np.arctan(number))
+    return res
+
+
 def localize_to_utc(time, location):
     """
     Converts or localizes a time series to UTC.