Added a new function to calculate nth fibonacci number using golden r… (

#222)

* Added a new function to calculate nth fibonacci number using golden ratio, Closes:#221

Signed-off-by: Mukul Bindal <[email protected]>

* Added validation and doc string.

Signed-off-by: Mukul Bindal <[email protected]>

---------

Signed-off-by: Mukul Bindal <[email protected]>
Co-authored-by: Mukul Bindal <[email protected]>

cereja/mathtools/_op.py

@@ -39,6 +39,7 @@
     "least_common_multiple",
     "degrees_to_radian",
     "radian_to_degrees",
+    "nth_fibonacci_number",
 ]
 
 
@@ -130,3 +131,24 @@ def degrees_to_radian(val):
 
 def radian_to_degrees(val):
     return (val * 180.0) / math.pi
+
+
+def nth_fibonacci_number(val:int) -> int:
+    """
+    Calculates the nth fibonacci number using the golden ratio formula.
+
+    Args:
+        val(int): The index (val>0) of the Fibonacci number to calculate
+    
+    Returns:
+        int: The nth Fibonacci number
+
+    Example:
+        >>> nth_fibonacci_number(10)
+        34
+    """
+    if val < 1:
+        raise ValueError("val should be greater than 0")
+    val -= 1 # First Fibonacci number is 0
+    phi = (1 + 5**0.5) / 2
+    return round(phi**val / 5**0.5)

tests/tests.py

@@ -37,7 +37,7 @@
 )
 from cereja.utils import is_iterable, is_sequence, chunk
 from cereja.array import prod
-from cereja.mathtools import theta_angle
+from cereja.mathtools import theta_angle, nth_fibonacci_number
 from cereja.config.cj_types import Number
 from cereja.mltools import Corpus
 from cereja.mltools.pln import LanguageData
@@ -158,6 +158,18 @@ def test_matrix(self):
         expected = Matrix([[1.0, 1.0, 1.0], [1.0, 1.0, 1.0]])
         self.assertTrue((a / b) == expected)
 
+    def test_nth_fibonacci_number(self):
+        with self.assertRaises(ValueError):
+            nth_fibonacci_number(-1)
+        self.assertEqual(nth_fibonacci_number(1), 0)
+        self.assertEqual(nth_fibonacci_number(2), 1)
+        self.assertEqual(nth_fibonacci_number(3), 1)
+        self.assertEqual(nth_fibonacci_number(4), 2)
+        self.assertEqual(nth_fibonacci_number(5), 3)
+        self.assertEqual(nth_fibonacci_number(10), 34)
+        self.assertEqual(nth_fibonacci_number(12), 89)
+        self.assertEqual(nth_fibonacci_number(20), 4181)
+
 
 class PathTest(unittest.TestCase):
     def test_sanity(self):