Will this work?
>>> x = (torch.rand((1,1,4,4)) * 2) - 1  # creating a tensor with a mixture of positive and negative value
>>> x
tensor([[[[ 0.8101, -0.5538,  0.2049, -0.8969],
          [-0.5394, -0.8587, -0.5657,  0.0481],
          [-0.9651,  0.8118, -0.3242, -0.5439],
          [ 0.0358, -0.1856, -0.1928,  0.7507]]]])
>>> min_x = torch.min(x[x>0]) # taking non-negative non-zero min value from the tensor
>>> min_x
tensor(0.0358)