# Fast convolution with striding step

I want to convolve two discrete functions $f$ and $g$ using convolution stride size $a$ to get the result as $s_{a, i}$:

$$s_{i,a} = \sum_i g_k f_{ai-k}$$

I know that simple convolution with $a=1$ can be calculated via FFT. I can do it even now, but I have to drop out all the points except $ai$. I think this way is not the best.

Cannot you advice me something better?

• Duplicate of math.stackexchange.com/questions/797870/… – Matt L. May 19 '14 at 12:12
• Certainly it is. I think, that DSP community can be even more relevant for it. – Felix May 19 '14 at 12:13
• You can use a polyphase implementation, as you already know. – Matt L. May 19 '14 at 12:14
• Yes, but I'm not sure if it will be the fastest solution. Nevertheless, thank your for you aid. – Felix May 19 '14 at 12:19