Some parallel computation questions

Question

I have some "print" statements. How do I execute them only on one process, say the one with rank 0 ?

I am modifying a Function like this

up1.vector()[:] += 0.01 * uppert.vector().array()

This gives error in parallel

RuntimeError: index must belong to this process, cannot index
off-process entries in a GenericVector

How can I make this correct for parallel computations ?

I read initial conditions from a file

  ups = Function(self.X)
  File("steady.xml") >> ups.vector()

Will this work correctly in parallel if steady.xml was generated by a serial run ?

Answer 1

1. use an if statement:

   if(MPI.process_number() > 0):
   print 'hello'

2. This looks funny to me... when I do it I do something like
   up_old.vector()[:] = up.vector()
   -> keep the .array(), which gives a numpy array, out of it. Does this statement usually work? You might want to look into axpy() too.. which I think keeps it all in vectors.

3. no idea. Try it!!

Comments

Thanks. Using .array() seemed to work but not in parallel. If I do as you suggest, it works in parallel also.