# How can I perform element wise multiplication of two tensors?

Given A tensor a with shape is (128,1,143) and another tensor b with shape of (128,80,134), and I want to perform an element wise multiplication. Then i tried the following ways:

1. a * b but it displayed an error of dimension mismatch
2. b * a.expand_as(b) but it also come up with error that dimension mismatch

can any one suggest me a solutions?

Hi,

Your tensors don’t have the same size. How do you match the elements to do element-wise operations?

Is there any way to make the tensors to have the same size, either a become similar size with b or b become similar size with a?

Well that depends where they come from and what they contain?
The size should have a meaning, you need to check what is this meaning in your case.

I apply the conv1d to speech recognition, the input is 13 dimensional fbank features, before providing the input to conv layer, i used x=x.view(batch, 1, seq_len), with batch size is 128, out channel is 1 and seq_len is 143 . Then apply conv with a filter size of 80 and got the tensor shape of (128, 80, 134). Here i like to add highway component to have highwayconv. Thus, I apply the sigmoid operation on the output of conv and get k, the apply element wise multiplication operation of k with conv output and get the transformation gate t shape is similar with conv. Next, subtraction operation of k from 1 and got tensor c with shape similar to conv, finally, when i do element wise multiplication operation of tensor c with the input x the dimension miss match occur?
Look the dimension sequence of the above operations:

1. 128,1,143 [input -x]
2. 128,80,134 [conv operation output tensor]
3. 128,80,134 [size of k tensor]
4. 128,80,134 [size of t tensor]
5. 128,80,134 [size of c tensor ]
When the sixth operation is fails due to the size miss match. Thus, i want to make the two tensors to have similar size and perform element wise multiplication?

It looks like you’re missing padding in your convolution to make sure that the output sequence length is the same as the output sequence length. For that you need a padding equal to half the kernel size.
You will still have a mismatch in size in the channel dimension, from what I remember, highway component are usually used for conv that have the same number of input and output channels to avoid this issue. In your case, I guess you can expand the input to be same size as the output if you really want to do this.