Fixed matrix multiplication, added input checks

matrix/matrix_multiplication_addition.py

@@ -1,6 +1,12 @@
 def add(matrix_a, matrix_b):
-    rows = len(matrix_a)
-    columns = len(matrix_a[0])
+    if not is_matrix(matrix_a) or not is_matrix(matrix_b):
+        raise ValueError('One or more of the arguments of multiply is not a matrix!')
+    size_a = matrix_size(matrix_a)
+    size_b = matrix_size(matrix_b)
+    if size_a[0] != size_b[0] or size_a[1] != size_b[1]:
+        raise ValueError('Matrices are incompatible in size')
+    rows = size_a[0]
+    columns = size_a[1]
     matrix_c = []
     for i in range(rows):
         list_1 = []
@@ -14,30 +20,46 @@ def scalarMultiply(matrix , n):
     return [[x * n for x in row] for row in matrix]
 
 def multiply(matrix_a, matrix_b):
+    '''Returns the matrix product of two matrices, expressed as a list of lists'''
+
+    if not is_matrix(matrix_a) or not is_matrix(matrix_b):
+        raise ValueError('One or more of the arguments of multiply is not a matrix!')
+    size_a = matrix_size(matrix_a)
+    size_b = matrix_size(matrix_b)
+    if(not size_a[0] == size_b[1]):
+        raise ValueError('Matrices are incompatible in size')
     matrix_c = []
-    n = len(matrix_a)
-    for i in range(n):
-        list_1 = []
-        for j in range(n):
-            val = 0
-            for k in range(n):
-                val = val + matrix_a[i][k] * matrix_b[k][j]
-            list_1.append(val)
-        matrix_c.append(list_1)
+    iteration_num = 0
+
+    for i in range(size_a[0]):
+        row_c = []
+        for j in range(size_b[1]):
+            element_c = 0
+            #We previously checked that the number of columns in a is the number of rows in b
+            for k in range(size_a[1]):
+                element_c += matrix_a[i][k] * matrix_b[k][j]
+            row_c.append(element_c)
+        matrix_c.append(row_c)
     return matrix_c
 
 def identity(n):
     return [[int(row == column) for column in range(n)] for row in range(n)] 
 
 def transpose(matrix):
+    if not is_matrix(matrix):
+        raise ValueError('Argument is not a matrix!')
     return map(list , zip(*matrix))
 
 def minor(matrix, row, column):
+    if not is_matrix(matrix):
+        raise ValueError('Argument is not a matrix!')
     minor = matrix[:row] + matrix[row + 1:]
     minor = [row[:column] + row[column + 1:] for row in minor]
     return minor
 
 def determinant(matrix):
+    if not is_matrix(matrix):
+        raise ValueError('Argument is not a matrix!')
     if len(matrix) == 1: return matrix[0][0]
 
     res = 0
@@ -46,6 +68,8 @@ def determinant(matrix):
     return res
 
 def inverse(matrix):
+    if not is_matrix(matrix):
+        raise ValueError('Argument is not a matrix!')
     det = determinant(matrix)
     if det == 0: return None
 
@@ -57,15 +81,56 @@ def inverse(matrix):
     cofactors = [[x * (-1) ** (row + col) for col, x in enumerate(matrixMinor[row])] for row in range(len(matrix))]
     adjugate = transpose(cofactors)
     return scalarMultiply(adjugate , 1/det)
+
+def check_matrix_size_consistency(matrix):
+    '''Checks that each row in a matrix has the same number of elements'''
+    if(is_list(matrix)):
+        for element in matrix:
+            if(not is_list(element)):
+                return False
+            if(len(matrix[0]) != len(element)):
+                return False
+    return True;
+
+def is_list(element):
+    '''Checks is a variable is a list'''
+    return isinstance(element, list)
+
+def is_int_or_float(element):
+    '''Checks is a variable is an int or a float'''
+    isinstance(element, (int, float))
+
+def is_matrix(matrix):
+    '''Checks is a variable is a matrix'''
+    #A variable is a matrix if and only if it is a list of lists of numbers (ints or floats)
+    if(is_list(matrix)):
+        for row in matrix:
+            if(is_list(row)):
+                for element in row:
+                    if(not is_int_or_float(element)):
+                        return False
+            else:
+                return False
+    else:
+        return False
+    return True
+
+def matrix_size(matrix):
+    '''Returns the size of a matrix as a list [rows, columns]'''
+    if(not is_matrix(matrix)):
+       raise ValueError('argument is not a matrix!')
+    return [len(matrix), len(matrix[0])]
 
 def main():
     matrix_a = [[12, 10], [3, 9]]
     matrix_b = [[3, 4], [7, 4]]
     matrix_c = [[11, 12, 13, 14], [21, 22, 23, 24], [31, 32, 33, 34], [41, 42, 43, 44]]
     matrix_d = [[3, 0, 2], [2, 0, -2], [0, 1, 1]]
+    matrix_e = [ [1, 2], [2, 1] , [1, 1]]
+    matrix_f = [ [1, 2, 5], [2, 1, 1] ]
 
     print(add(matrix_a, matrix_b))
-    print(multiply(matrix_a, matrix_b))
+    print(multiply(matrix_e, matrix_f))
     print(identity(5))
     print(minor(matrix_c , 1 , 2))
     print(determinant(matrix_b))