Removed in LÖVE 0.8.0  
 It has been replaced with ParticleSystem:setSizes. 
Sets the size of the particle (1.0 being normal size). The particles will grow/shrink from the starting size to the ending size. The variation affects starting size only.
ParticleSystem:setSize( min, max, variation )
number minnumber max (min)number variation (1)Nothing.
 
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Licensed under the GNU Free Documentation License, Version 1.3.
    https://love2d.org/wiki/ParticleSystem:setSize