Created Sherman Morrison method

matrix/sherman_morrison.py

@@ -0,0 +1,161 @@
+class Matrix:
+    """
+    <class Matrix>
+    Matrix structure.
+    """
+
+    def __init__(self, row: int, column: int, default_value: float = 0):
+        """
+        <method Matrix.__init__>
+        Initialize matrix with given size and default value.
+        """
+
+        self.row, self.column = row, column
+        self.array = [[default_value for c in range(column)] for r in range(row)]
+
+    def __str__(self):
+        """
+        <method Matrix.__str__>
+        Return string representation of this matrix.
+        """
+
+        # Prefix
+        s = "Matrix consist of %d rows and %d columns\n" % (self.row, self.column)
+
+        # Make string identifier
+        max_element_length = 0
+        for row_vector in self.array:
+            for obj in row_vector:
+                max_element_length = max(max_element_length, len(str(obj)))
+        string_format_identifier = "%%%ds" % (max_element_length,)
+
+        # Make string and return
+        for row_vector in self.array:
+            s += "["
+            s += ", ".join(string_format_identifier % (obj,) for obj in row_vector)
+            s += "]\n"
+        return s
+
+    def __getitem__(self, loc: tuple):
+        """
+        <method Matrix.__getitem__>
+        Return array[row][column] where loc = (row, column).
+        """
+        assert(isinstance(loc, (list, tuple)) and len(loc) == 2)
+        assert(0 <= loc[0] < self.row and 0 <= loc[1] < self.column)
+        return self.array[loc[0]][loc[1]]
+
+    def __setitem__(self, loc: tuple, value: float):
+        """
+        <method Matrix.__setitem__>
+        Set array[row][column] = value where loc = (row, column).
+        """
+        assert(isinstance(loc, (list, tuple)) and len(loc) == 2)
+        assert(0 <= loc[0] < self.row and 0 <= loc[1] < self.column)
+        self.array[loc[0]][loc[1]] = value
+
+    def __add__(self, another):
+        """
+        <method Matrix.__add__>
+        Return self + another.
+        """
+
+        # Validation
+        assert(self.row == another.row and self.column == another.column)
+        assert(isinstance(another, Matrix))
+
+        # Add
+        result = Matrix(self.row, self.column)
+        for r in range(self.row):
+            for c in range(self.column):
+                result[r,c] = self[r,c] + another[r,c]
+        return result
+
+    def __neg__(self):
+        """
+        <method Matrix.__neg__>
+        Return -self.
+        """
+
+        result = Matrix(self.row, self.column)
+        for r in range(self.row):
+            for c in range(self.column):
+                result[r,c] = -self[r,c]
+        return result
+
+    def __sub__(self, another): return self + (-another)
+
+    def __mul__(self, another):
+        """
+        <method Matrix.__mul__>
+        Return self * another.
+        """
+
+        if isinstance(another, (int, float)): # Scalar multiplication
+            result = Matrix(self.row, self.column)
+            for r in range(self.row):
+                for c in range(self.column):
+                    result[r,c] = self[r,c] * another
+            return result
+        elif isinstance(another, Matrix): # Matrix multiplication
+            assert(self.column == another.row)
+            result = Matrix(self.row, another.column)
+            for r in range(self.row):
+                for c in range(another.column):
+                    for i in range(self.column):
+                        result[r,c] += self[r,i] * another[i,c]
+            return result
+        else: raise TypeError("Unsupported type given for another (%s)" % (type(another),))
+
+    def transpose(self):
+        """
+        <method Matrix.transpose>
+        Return self^T.
+        """
+
+        result = Matrix(self.column, self.row)
+        for r in range(self.row):
+            for c in range(self.column):
+                result[c,r] = self[r,c]
+        return result
+
+    def ShermanMorrison(self, u, v):
+        """
+        <method Matrix.ShermanMorrison>
+        Apply Sherman-Morrison formula in O(n^2).
+        To learn this formula, please look this: https://en.wikipedia.org/wiki/Sherman%E2%80%93Morrison_formula
+        This method returns (A + uv^T)^(-1) where A^(-1) is self. Returns None if it's impossible to calculate.
+        Warning: This method doesn't check if self is invertible. 
+            Make sure self is invertible before execute this method.
+        """
+
+        # Size validation
+        assert(isinstance(u, Matrix) and isinstance(v, Matrix))
+        assert(self.row == self.column == u.row == v.row) # u, v should be column vector
+        assert(u.column == v.column == 1) # u, v should be column vector
+
+        # Calculate
+        vT = v.transpose()
+        numerator_factor = (vT * self * u)[0, 0] + 1
+        if numerator_factor == 0: return None # It's not invertable
+        return self - ((self * u) * (vT * self) * (1.0 / numerator_factor))
+
+# Testing
+if __name__ == "__main__":
+
+    # a^(-1)
+    ainv = Matrix(3, 3, 0)
+    for i in range(3): ainv[i,i] = 1
+    print("a^(-1) is %s" % (ainv,))
+
+    # u, v
+    u = Matrix(3, 1, 0)
+    u[0,0], u[1,0], u[2,0] = 1, 2, -3
+    v = Matrix(3, 1, 0)
+    v[0,0], v[1,0], v[2,0] = 4, -2, 5
+    print("u is %s" % (u,))
+    print("v is %s" % (v,))
+    print("uv^T is %s" % (u * v.transpose()))
+
+    # Sherman Morrison
+    print("(a + uv^T)^(-1) is %s" % (ainv.ShermanMorrison(u, v),))