Multiplying every 3 elements by a vector?
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? M _________________________________________________________________ Need to know now? Get instant answers with Windows Live Messenger. http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGLM_WL...
On Wed, Jul 9, 2008 at 1:16 PM, Marlin Rowley <marlin_rowley@hotmail.com> 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 1D. Chuck
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: charlesr.harris@gmail.comTo: numpydiscussion@scipy.orgSubject: Re: [Numpydiscussion] Multiplying every 3 elements by a vector? On Wed, Jul 9, 2008 at 1:16 PM, Marlin Rowley <marlin_rowley@hotmail.com> 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 1D.Chuck _________________________________________________________________ Use video conversation to talk facetoface with Windows Live Messenger. http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGLM_WL...
On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <marlin_rowley@hotmail.com> 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
2008/7/9 Charles R Harris <charlesr.harris@gmail.com>:
On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <marlin_rowley@hotmail.com> 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
On Wed, Jul 9, 2008 at 3:26 PM, Anne Archibald <peridot.faceted@gmail.com> wrote:
2008/7/9 Charles R Harris <charlesr.harris@gmail.com>:
On Wed, Jul 9, 2008 at 2:34 PM, Marlin Rowley <marlin_rowley@hotmail.com
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
participants (3)

Anne Archibald

Charles R Harris

Marlin Rowley