Increased damage vs more damage

How does increased damage of different types add up together?

Let's say I have a fire spell that deals 1000 dps base damage. I then pick up 100% increased fire damage and 100% increased elemental damage on the passive tree.

Do fire and elemental increases add up together to a single 200% increase, as in:
1000 * (1 + (100% fire + 100% elemental)/100) = 3000 dps?

Or do they add up separately to two different increases, for two separate 100% increases, as in:
1000 * (1 + 100% fire/100) * (1 + 100% elemental/100) = 4000 dps?

So I understand it as:

with considering only increase and more modifiers

total_damage = base_damage * (1 + Σ increase_modifier) * Π (1 + more_modifier)

am I right?