In this example:
short sell 145 DGAZ
short sell 50 UGAZ
This idea can be found using cointegration methods as well, though I used another method that run an optimization that spits out weights -- useful for a large number of assets.
The weights are 50-50 because the two assets are 1) highly correlated (~ minus 1), 2) bear the same leverage (3x) and 3) the expected return of the underlyings are negative, thus suggesting negative weightings.
The and its mean are showed below.