Add gradients for uncertainty handling.

pymagglobal/utils.py

@@ -39,6 +39,32 @@ def _nicelabel(label):
     return fr'${parts[0]}$ {parts[1]}'
 
 
+def grad_d(n, e, z):
+    '''Calculate the gradient of D.
+    '''
+    res = np.column_stack((-e, n, np.zeros_like(n)))
+    res /= (n**2 + e**2)[:, np.newaxis]
+    return np.rad2deg(res)
+
+
+def grad_i(n, e, z):
+    '''Calculate the gradient of I.
+    '''
+    res = -np.column_stack((n, e, z)) \
+        * z[:, np.newaxis]
+    res /= (n**2 + e**2 + z**2)[:, np.newaxis]
+    res[:, 2] += 1.
+    res /= np.sqrt(n**2 + e**2)[:, np.newaxis]
+    return np.rad2deg(res)
+
+
+def grad_f(n, e, z):
+    '''Calculate the gradient of F '''
+    res = np.column_stack((n, e, z))
+    res /= np.sqrt(n**2 + e**2 + z**2)[:, np.newaxis]
+    return res
+
+
 def nez2dif(n, e, z):
     '''Transform the magnetic field components north, east and vertically
     downward to declination, inclination and intensity.