Shares in Simulations Plus Inc. closed up 8 percent Tuesday after the Lancaster-based software developer announced a purchase order from the Environmental Protection Agency for its Admet Predictor software. The company did not specify the dollar value of the order. This was the first order for Simulations Plus from the EPA. The software will allow the EPA to predict potential toxicities of industry chemicals, agricultural chemicals, and drug molecules, the company said in a statement. Shares rose to $2.30 but quickly retreated in after-hours trading, dropping 4.7 percent to $1.93.