Re: [Numpy-discussion] Multiplying every 3 elements by a vector?
On Wed, Jul 9, 2008 at 3:26 PM, Anne Archibald <[EMAIL PROTECTED]> wrote: > 2008/7/9 Charles R Harris <[EMAIL PROTECTED]>: > > > > On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <[EMAIL PROTECTED] > > > > wrote: > >> > >> Thanks Chuck, but I wasn't quit clear with my question. > >> > >> You answered exactly according to what I asked, but I failed to mention > >> needing the dot product instead of just the product. > >> > >> So, > >> > >> v dot A = v' > >> > >> v'[0] = v[0]*A[0] + v[1]*A[1] + v[2]*A[2] > >> v'[1] = v[0]*A[3] + v[1]*A[4] + v[2]*A[5] > >> v'[2] = v[0]*A[6] + v[1]*A[7] + v[2]*A[8] > >> > > > > There is no built in method for this specific problem (stacks of vectors > and > > matrices), but you can make things work: > > > > sum(A.reshape((-1,3))*v, axis=1) > > > > You can do lots of interesting things using such manipulations and > newaxis. > > For instance, multiplying stacks of matrices by stacks of matrices etc. I > > put up a post of such things once if you are interested. > > This particular instance can be viewed as a matrix multiplication > (np.dot(A.reshape((-1,3)),v) I think). Yep, that should work. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Multiplying every 3 elements by a vector?
2008/7/9 Charles R Harris <[EMAIL PROTECTED]>: > > On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <[EMAIL PROTECTED]> > wrote: >> >> Thanks Chuck, but I wasn't quit clear with my question. >> >> You answered exactly according to what I asked, but I failed to mention >> needing the dot product instead of just the product. >> >> So, >> >> v dot A = v' >> >> v'[0] = v[0]*A[0] + v[1]*A[1] + v[2]*A[2] >> v'[1] = v[0]*A[3] + v[1]*A[4] + v[2]*A[5] >> v'[2] = v[0]*A[6] + v[1]*A[7] + v[2]*A[8] >> > > There is no built in method for this specific problem (stacks of vectors and > matrices), but you can make things work: > > sum(A.reshape((-1,3))*v, axis=1) > > You can do lots of interesting things using such manipulations and newaxis. > For instance, multiplying stacks of matrices by stacks of matrices etc. I > put up a post of such things once if you are interested. This particular instance can be viewed as a matrix multiplication (np.dot(A.reshape((-1,3)),v) I think). Anne ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Multiplying every 3 elements by a vector?
On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <[EMAIL PROTECTED]> wrote: > Thanks Chuck, but I wasn't quit clear with my question. > > You answered exactly according to what I asked, but I failed to mention > needing the dot product instead of just the product. > > So, > > v dot A = v' > > v'[0] = v[0]*A[0] + v[1]*A[1] + v[2]*A[2] > v'[1] = v[0]*A[3] + v[1]*A[4] + v[2]*A[5] > v'[2] = v[0]*A[6] + v[1]*A[7] + v[2]*A[8] > > There is no built in method for this specific problem (stacks of vectors and matrices), but you can make things work: sum(A.reshape((-1,3))*v, axis=1) You can do lots of interesting things using such manipulations and newaxis. For instance, multiplying stacks of matrices by stacks of matrices etc. I put up a post of such things once if you are interested. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Multiplying every 3 elements by a vector?
Thanks Chuck, but I wasn't quit clear with my question. You answered exactly according to what I asked, but I failed to mention needing the dot product instead of just the product. So, v dot A = v' v'[0] = v[0]*A[0] + v[1]*A[1] + v[2]*A[2] v'[1] = v[0]*A[3] + v[1]*A[4] + v[2]*A[5] v'[2] = v[0]*A[6] + v[1]*A[7] + v[2]*A[8] -M Date: Wed, 9 Jul 2008 13:26:01 -0600From: [EMAIL PROTECTED]: [EMAIL PROTECTED]: Re: [Numpy-discussion] Multiplying every 3 elements by a vector? On Wed, Jul 9, 2008 at 1:16 PM, Marlin Rowley <[EMAIL PROTECTED]> wrote: All: I'm trying to take a constant vector: v = (0.122169, 0.61516, 0.262671) and multiply those values by every 3 components in an array of length N: A = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ] So what I want is: v[0]*A[0]v[1]*A[1]v[2]*A[2]v[0]*A[3]v[1]*A[4]v[2]*A[5]v[0]*A[6] ... How do I do this with one command in numPy? If the length of A is divisible by 3:A.reshape((-1,3))*vYou might want to reshape the result to 1-D.Chuck _ Use video conversation to talk face-to-face with Windows Live Messenger. http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGLM_WL_Refresh_messenger_video_072008___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Multiplying every 3 elements by a vector?
On Wed, Jul 9, 2008 at 1:16 PM, Marlin Rowley <[EMAIL PROTECTED]> wrote: > All: > > I'm trying to take a constant vector: > > v = (0.122169, 0.61516, 0.262671) > > and multiply those values by every 3 components in an array of length N: > > A = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ] > > So what I want is: > > v[0]*A[0] > v[1]*A[1] > v[2]*A[2] > v[0]*A[3] > v[1]*A[4] > v[2]*A[5] > v[0]*A[6] > > ... > > How do I do this with one command in numPy? > > If the length of A is divisible by 3: A.reshape((-1,3))*v You might want to reshape the result to 1-D. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
