Hi all,
pytorch 0.3.1 here.
I have some variables:
x = ag.Variable(torch.ones(1, 1), requires_grad = True)
y = ag.Variable(torch.ones(1, 1), requires_grad = True)
z = ag.Variable(torch.ones(1, 1), requires_grad = True)

I then create a variable representing their concatenation:
w = torch.cat([x, y, z])
f = x + y + z
Then I try to take derivatives:
ag.grad(f, x, retain_graph=True, create_graph=True)
This is fine and returns 1, as expected.  Same for y and z.
However,

ag.grad(f, w, retain_graph=True, create_graph=True)

Returns an error: RuntimeError: differentiated input is unreachable
Of course that makes sense - w is not explicitly used in the declaration of f.  However, I’d like a behavior where one line of code can generate something like [1; 1; 1] as output.
Let’s say I wanted to conveniently batch my variables together, and then take the gradient of the whole shebang at once, rather than processing variables independently (which can make bookkeeping a nightmare).  Is there any way to get the outcome I desire?