mat1 and mat2 shapes cannot be multiplied

This error message typically occurs when you are trying to perform matrix multiplication on two matrices with incompatible shapes. In order to multiply two matrices, the number of columns in the first matrix must match the number of rows in the second matrix.

For example, if you have a matrix `mat1` with shape `(3, 4)` and a matrix `mat2` with shape `(4, 2)`, you can perform matrix multiplication like this:

result = mat1.dot(mat2)

The resulting matrix will have shape `(3, 2)`.

If the shapes of the matrices do not match, you will get the "shapes cannot be multiplied" error. To fix this, you may need to transpose one of the matrices or reshape them to have compatible dimensions.