This is not a case of only ask a question if you know the answer by the way...so I expect to make Mars suitable for us..er some of us

we need a few things and I have become somewhat focused on the need for an atmosphere which cant be that hard to make but keeping it would mean we would need more gravity to hold on to it I imagine...wanting to help I started thinking about how we could increase gravity..add more mass no doubt but that may not be necessary if we could increase rotational speed..but would that do it?.. intuitively I am torn between gravity increasing on the one hand or stuff being thrown off into space on the other...my limited understanding of GR does not equip me to work out the math but does anyone have any ideas?
No doubt Elron has it worked out ..does he I wonder.
alex