other/integeration_by_simpson_approx.py is added for approximate integeration

other/integeration_by_simpson_approx.py

@@ -0,0 +1,123 @@
+"""
+Author : Syed Faizan ( 3rd Year IIIT Pune )
+Github : faizan2700
+
+Purpose : You have one function f(x) which takes float integer and returns
+float you have to integrate the function in limits a to b.
+The approximation proposed by Thomas Simpsons in 1743 is one way to calculate integration.
+
+( read article : https://cp-algorithms.com/num_methods/simpson-integration.html )
+
+simpson_integration() takes function,lower_limit=a,upper_limit=b,precision and
+returns the integration of function in given limit.
+"""
+
+# constants
+# the more the number of steps the more accurate
+N_STEPS = 1000
+
+
+def f(x: float) -> float:
+    return x * x
+
+
+"""
+Summary of Simpson Approximation :
+
+By simpsons integration :
+1.integration of fxdx with limit a to b is = f(x0) + 4 * f(x1) + 2 * f(x2) + 4 * f(x3) + 2 * f(x4)..... + f(xn)
+where x0 = a
+xi = a + i * h
+xn = b
+"""
+
+
+def simpson_integration(function, a: float, b: float, precision: int = 4) -> float:
+
+    """
+    Args:
+        function : the function which's integration is desired
+        a : the lower limit of integration
+        b : upper limit of integraion
+        precision : precision of the result,error required default is 4
+
+    Returns:
+        result : the value of the approximated integration of function in range a to b
+
+    Raises:
+        AssertionError: function is not callable
+        AssertionError: a is not float or integer
+        AssertionError: function should return float or integer
+        AssertionError: b is not float or integer
+        AssertionError: precision is not positive integer
+
+    >>> simpson_integration(lambda x : x*x,1,2,3)
+    2.333
+
+    >>> simpson_integration(lambda x : x*x,'wrong_input',2,3)
+    Traceback (most recent call last):
+        ...
+    AssertionError: a should be float or integer your input : wrong_input
+
+    >>> simpson_integration(lambda x : x*x,1,'wrong_input',3)
+    Traceback (most recent call last):
+        ...
+    AssertionError: b should be float or integer your input : wrong_input
+
+    >>> simpson_integration(lambda x : x*x,1,2,'wrong_input')
+    Traceback (most recent call last):
+        ...
+    AssertionError: precision should be positive integer your input : wrong_input
+    >>> simpson_integration('wrong_input',2,3,4)
+    Traceback (most recent call last):
+        ...
+    AssertionError: the function(object) passed should be callable your input : wrong_input
+
+    >>> simpson_integration(lambda x : x*x,3.45,3.2,1)
+    -2.8
+
+    >>> simpson_integration(lambda x : x*x,3.45,3.2,0)
+    Traceback (most recent call last):
+        ...
+    AssertionError: precision should be positive integer your input : 0
+
+    >>> simpson_integration(lambda x : x*x,3.45,3.2,-1)
+    Traceback (most recent call last):
+        ...
+    AssertionError: precision should be positive integer your input : -1
+
+    """
+    assert callable(
+        function
+    ), f"the function(object) passed should be callable your input : {function}"
+    assert isinstance(a, float) or isinstance(
+        a, int
+    ), f"a should be float or integer your input : {a}"
+    assert isinstance(function(a), float) or isinstance(
+        function(a), int
+    ), f"the function should return integer or float return type of your function, {type(a)}"
+    assert isinstance(b, float) or isinstance(
+        b, int
+    ), f"b should be float or integer your input : {b}"
+    assert (
+        isinstance(precision, int) and precision > 0
+    ), f"precision should be positive integer your input : {precision}"
+
+    # just applying the formula of simpson for approximate integraion written in
+    # mentioned article in first comment of this file and above this function
+
+    h = (b - a) / N_STEPS
+    result = function(a) + function(b)
+
+    for i in range(1, N_STEPS):
+        a1 = a + h * i
+        result += function(a1) * (4 if i%2 else 2)
+
+    result *= h / 3
+    return round(result, precision)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()