# Re: rho vs. rho +/- 1 (esp. for computePressureField())

OpenLB – Open Source Lattice Boltzmann Code › Forums › on OpenLB › General Topics › rho vs. rho +/- 1 (esp. for computePressureField()) › Re: rho vs. rho +/- 1 (esp. for computePressureField())

Dear Randy,rnrn1) Why do you do this? Does this yield a more stable or accurate simulation?rnA: Yes indeed, we win one or more order of magnitude for the representation of the distribution function f which leads to more stability and accuracy. This is because f-f^eq is small and will be distributed around zero while f is distributes around f^eq which is not zero.rn2) Why is pressure calculated the way it is (shown below)? Isn’t the equation of staternp = rho/c^2,rnnotrnp = (rho-1)/c^2rnA: Have a look at some standard text books on LBM or “Lattice Boltzmann Model for the Incompressible Navier–Stokes“. In the later paper of He/Lou it is explained very nicely in my opinion. rnrnMathias