Defensive Matrix (Matrix or D-Matrix for short) is a defensive spell cast by the Terran Science Vessel. It creates a 250 Hit Point non-regenerating shield around the target unit. After about 60 seconds, the effect wears off even if the shields haven't run out of Hit Points. Defensive Matrix "has" 0 armor and absorbs full damage of every damage type like protoss shields. Note that 0,5 damage "leaks" through the Defensive Matrix from every hit as in the case where armor of the target is bigger than damage. Cloaked units surrounded by a D-Matrix are automatically detected by any enemy units. Using D-Matrix more than once on a unit will replace any old Matrix with the new one - you can't "stack" D-Matrices.  Matrixes count as having priority over shields, so health will appear to go down first on Protoss units.
Defense Matrix is an occasional spell, and mostly used only if the situation requires it. Being the default spell it is always at hand when Vessels come into play, but usually the energy is preferably used for the stronger spells Irradiate and EMP Shockwave. When it is used it functions to save high-priority units like Siege Tanks and Battlecruisers and key units that are, for example, blocking a choke or ramp or to protect a key dropship flying into an enemy base.
Vessels are generally excluded from this match-up because of the high gas cost of other units. When they do come into play it is usually to deploy EMP as a counter to Battlecruisers. Use of Matrix only occurs situationally.
Although Vessels are more common in this match-up, energy is usually needed for EMP. Occasionally though, Matrix is used on the front-most Tank as Zealots charge the Terran lines. Prolonging the life of this single Tank can be key as the other Tanks can fire longer at the Zealots before the latter move on to attacking other Tanks.
Defensive Matrix is most often seen in this match-up. In battles that are mostly low HP/low damage units fighting each other, an additional 250 HP can make a huge difference. Also, when backing away from a Swarm, Tanks can be Matrixed to protect them as they unsiege and back away.
As Scourge usually patrol the Zerg base, a Dropship - dies to 2 Scourge hits - has a hard time getting in. Defensive Matrix will help Dropships reach their destination and even some builds incorporate this tactic. See Stylish's FPVOD's: TvZ 9min Push on Othello for an example.
Matrix can be used to cleverly destroy a Lurker field. A single Marine is Matrixed and runs into (or on the sides of) the Lurkers to draw fire. When past the field, more Marines engage, now safe from splash damage, to take out the Lurkers - unless the Zerg player manually targets the attacking Marines, ignoring the D-Matrixed Marine. You can still draw away the first Lurker attack this way, unless the opponent manually stops the Lurkers from attacking, but this is very rarely the case.
In Combination with Other Spells
- Matrix will fully absorb damage from Feedback.
- Matrix will partly absorb damage from Psionic Storm and Yamato Cannon.
- Matrix will partly absorb damage from Irradiate. To Protoss units, damage that is done is inflicted directly to the HP.
- Matrix will not absorb damage from Plague, Stim Pack or EMP Shockwave.
- Matrixed units can still be Stasised, Lockdowned and Maelstromed. Units in Stasis cannot be Matrixed. Matrix will remain active in Lockdown and Maelstrom.
- Matrix will dispel Hallucinations.
- Matrix can not be dispelled with Restoration.
- Science Vessels can't Matrix themselves.
- Matrix will stay active on Hydralisks morphing into a Lurker and Mutalisks morphing to Guardian or Devourer.
- Matrix will dispel on Drones morphing into a building.
- Firebathero vs Much - 08-10-11 - Clubday MSL 2008 Group phase - Firebathero uses Defensive Matrix as a taunt.
- Flash vs Jaedong - 2010-09-11 - Korean Air OSL 2 Grand Finals Flash uses Defensive Matrix on Firebats to help burn through Jaedong's defenses
- adapted from: Terran Special Abilities