Re: Numpy: Multiplying arrays of matrices
Hi, I assume you have arrays like these: import numpy as np m1 = np.random.rand(size=(4,3,3)) m2 = np.random.rand(size=(4,3,3)) So that m1[0] is a 3x3 Matrix and m1[1] is another one, i.e. you have four matrices. On 09/15/2010 01:54 AM, Gregory Ewing wrote: I had thought that dot() might do this, but it appears not, because e.g. applying it to two 3-d arrays gives a 4-d array, not another 3-d array. You now want to compute the matrixproducts like this np.dot(m1[0], m2[0]) and most likely you want to do this for all of the pairs m1m2 = np.array(map(lambda (a,b): np.dot(a,b), zip(m1,m2))) or you could write the loop m1m2 = np.empty_like(m1) for i in range(m1m2.shape[0]): ... m1m2[i] = np.dot(m1, m2) which might scale better I'd also like to be able to find the inverse of each matrix in one of these arrays, but again, inv() doesn't do what I want -- it only works on 2-d arrays. Same as before m1inv = np.array(map(np.linalg.inv, m1)) or writing the loop m1inv = np.empty_like(m1) for i in range(m1inv.shape[0]): ... m1inv[i] = np.linalg.inv(m1[i]) Once again, I'm not sure whether or not it is acceptable to have the overhead of treating the array as a list. Andre -- http://mail.python.org/mailman/listinfo/python-list
Re: Numpy: Multiplying arrays of matrices
On 09/16/2010 08:24 AM, Andre Alexander Bell wrote: or you could write the loop m1m2 = np.empty_like(m1) for i in range(m1m2.shape[0]): ... m1m2[i] = np.dot(m1, m2) This should have been ... m1m2[i] = np.dot(m1[i], m2[i]) Sorry for the typo. Andre -- http://mail.python.org/mailman/listinfo/python-list
Re: Numpy: Multiplying arrays of matrices
On 14-Sep-10 19:54 PM, Gregory Ewing wrote: Suppose I have two N+2 dimensional arrays, representing N-d arrays of 2-d matrices. I want to perform matrix multiplication between corresponding matrices in these arrays. I had thought that dot() might do this, but it appears not, because e.g. applying it to two 3-d arrays gives a 4-d array, not another 3-d array. I'd also like to be able to find the inverse of each matrix in one of these arrays, but again, inv() doesn't do what I want -- it only works on 2-d arrays. Any thoughts on how to achieve these things using numpy functions? There is a Matrix sub-class which permit you to do that sort of thimg. Colin W. -- http://mail.python.org/mailman/listinfo/python-list
Re: Numpy: Multiplying arrays of matrices
On Tue, Sep 14, 2010 at 7:54 PM, Gregory Ewing greg.ew...@canterbury.ac.nzwrote: Suppose I have two N+2 dimensional arrays, representing N-d arrays of 2-d matrices. I want to perform matrix multiplication between corresponding matrices in these arrays. I had thought that dot() might do this, but it appears not, because e.g. applying it to two 3-d arrays gives a 4-d array, not another 3-d array. I'd also like to be able to find the inverse of each matrix in one of these arrays, but again, inv() doesn't do what I want -- it only works on 2-d arrays. Any thoughts on how to achieve these things using numpy functions? Unrelated to numpy, but you can apply the basics of dynamic programming to optimize the stuff. -- Greg -- http://mail.python.org/mailman/listinfo/python-list -- ~l0nwlf -- http://mail.python.org/mailman/listinfo/python-list
Re: Numpy: Multiplying arrays of matrices
On 9/15/10 11:36 AM, Colin J. Williams wrote: On 14-Sep-10 19:54 PM, Gregory Ewing wrote: Suppose I have two N+2 dimensional arrays, representing N-d arrays of 2-d matrices. I want to perform matrix multiplication between corresponding matrices in these arrays. I had thought that dot() might do this, but it appears not, because e.g. applying it to two 3-d arrays gives a 4-d array, not another 3-d array. I'd also like to be able to find the inverse of each matrix in one of these arrays, but again, inv() doesn't do what I want -- it only works on 2-d arrays. Any thoughts on how to achieve these things using numpy functions? There is a Matrix sub-class which permit you to do that sort of thimg. No, it doesn't. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: Numpy: Multiplying arrays of matrices
On Sep 14, 4:54 pm, Gregory Ewing greg.ew...@canterbury.ac.nz wrote: Suppose I have two N+2 dimensional arrays, representing N-d arrays of 2-d matrices. I want to perform matrix multiplication between corresponding matrices in these arrays. I had thought that dot() might do this, but it appears not, because e.g. applying it to two 3-d arrays gives a 4-d array, not another 3-d array. I'd also like to be able to find the inverse of each matrix in one of these arrays, but again, inv() doesn't do what I want -- it only works on 2-d arrays. Any thoughts on how to achieve these things using numpy functions? I find for situations like this the best thing I can do is hand code the bounded operation and use the slicing to handle the arbitrarily large stuff with slicing. So, r[:,:,1,1] = a[:,:,1,1]*b[:,:,1,1] + a[:,:,2,1]*b[:,:,1,2] r[:,:,1,2] = a[:,:,1,2]*b[:,:,1,1] + a[:,:,2,2]*b[:,:,1,2] etc. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
