Attached is a patch that:
1) removes the .expand() call that was being done in matrix_multiply()
2) adds a doctest and improves the docstring
3) provides and alternative implementation that is somewhat clearer,
but about 5% slower.
~Luke
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From 994e7239dae0f2f7aab4cae57fdfdccb561edde1 Mon Sep 17 00:00:00 2001
From: Luke Peterson <hazelnu...@gmail.com>
Date: Sat, 8 Aug 2009 21:03:31 -0700
Subject: [PATCH] Removed .expand() in matrix_multiply, added doctests, alternate implementation
---
sympy/matrices/matrices.py | 44 +++++++++++++++++++++++++++++++++++++-------
1 files changed, 37 insertions(+), 7 deletions(-)
diff --git a/sympy/matrices/matrices.py b/sympy/matrices/matrices.py
index 72bb129..ae04a32 100644
--- a/sympy/matrices/matrices.py
+++ b/sympy/matrices/matrices.py
@@ -1474,20 +1474,50 @@ class Matrix(object):
count += 1
return v
-def matrix_multiply(A,B):
+def matrix_multiply(A, B):
"""
- Return A*B.
+ Matrix product A*B.
+
+ A and B must be of appropriate dimensions. If A is a m x k matrix, and B
+ is a k x n matrix, the product will be an m x n matrix.
+
+ Example:
+
+ >>> from sympy import Matrix
+ >>> A = Matrix([[1, 2, 3], [4, 5, 6]])
+ >>> B = Matrix([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
+ >>> A*B
+ [30, 36, 42]
+ [66, 81, 96]
+ >>> B*A
+ Traceback (most recent call last):
+ ...
+ ShapeError
+ >>>
"""
+ # The following implmentation is equivalent, but about 5% slower
+ #ma, na = A.shape
+ #mb, nb = B.shape
+ #
+ #if na != mb:
+ # raise ShapeError()
+ #product = Matrix(ma, nb, lambda i,j: 0)
+ #for i in xrange(ma):
+ # for j in xrange(nb):
+ # s = 0
+ # for k in range(na):
+ # s += A[i, k]*B[k, j]
+ # product[i, j] = s
+ #return product
if A.shape[1] != B.shape[0]:
raise ShapeError()
blst = B.T.tolist()
alst = A.tolist()
- return Matrix(A.shape[0], B.shape[1], lambda i,j:
- reduce(lambda k,l: k+l,
- map(lambda n,m: n*m,
+ return Matrix(A.shape[0], B.shape[1], lambda i, j:
+ reduce(lambda k, l: k+l,
+ map(lambda n, m: n*m,
alst[i],
- blst[j])).expand())
- # .expand() is a test
+ blst[j])))
def matrix_add(A,B):
"""Return A+B"""
--
1.6.0.4
