I was wondering if it was possible to parametrize matrices such that zygote’s gradient would only be performed on the selected coefficients of the matrix.

Some dummy code would look like:

```
theta = randn(2)
W = [theta[1] theta[2]; 0.0 theta[1]]
b = randn(100)
x = randn(2, 100)
gs = gradient(w -> sum(w*x+b), W)
```

However the gradient would only be performed on the values of theta, keeping W[2, 1] set to 0.0 for the entire gradient descent. Also this would imply that the gradients for theta[1] and theta[2] be equal at all times.

Am I completely going at this wrong way? or is it just not possible in julia?