Extract Parameter beside Velocity

Hello Dears,

I am totally new to Palabos. I working on a project where I have to extract additional parameters beside velocity such as pressure and strain.

I started with the provided examples that comes with Palabos, but I still have some difficulty.

At this point, I am trying to extract pressure beside velocity from the cavity3d example. Would any one please advise me how to achieve this goal ? How can I start? and what things should I understand before starting solving this ?

I tried to add this line in the cavity3d.cpp:
**vtkOut.writeData(computePressure(lattice), “pressure”, util::sqr(dx/dt)fluidDensity);

But I got this error:
error: ‘computePressure’ was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
*computeNorm(computePressure (
*computePressure(lattice) ), slice ),

Any advice and help and suggestion would be seriously appreciate it.
Thank you in advance