adding function to estimate fold hinge location

finds the roots of the function for a given range and step size.
Start looking at range[0] + step find root, then look at range[0]+step,
to range[0]+2*step while <range[1]
note the step should be smaller than the wavelength

Author: lachlangrose

LoopStructural/modelling/fold/fold_rotation_angle.py

@@ -130,4 +130,18 @@ def set_function(self, function):
         -------
 
         """
-        self. fold_rotation_function = function
+        self. fold_rotation_function = function
+
+    def find_hinges(self,range,step):
+        
+        import scipy.optimize as optimize
+        def fra(x):
+            x = np.array([x])
+            return self.__call__(x)
+        roots = []
+        x = range[0]
+        while x < range[1]:
+            result = optimize.root_scalar(fra,bracket=[x,x+step])
+            roots.append(result.root)
+            x+=step
+        return roots