How_can_I_provide_a_solvable_MeqParm_with_the_value_of_another_node_as_an_'initial_guess'?

Well, at the moment there's no easy way to tell a Meq.Parm to get its initial value from another node (which is what you're essentially trying to do here).

We must think of providing one cleanly. In the meantime, I suggest a Really Ugly Kludge:

1. Form up a set of condeqs with your constants on one side, and the Parms you want to initialize on the other side.

2. Attach another solver to them (let's call it the pre-solver).

3. Put a reqseq below the solvers, so that you fire up the pre-solver first, then the real thing.

This way you will make it solve a set of equations of the form {x=a} first. Hopefully that should be done in a few iterations, and then your Parms are all primed. This has got to be the ugliest way to assign a value in the entire history of numerical computing! Still, it should get the job done...

This code fragment gives an example:

def create_polc(c00=0.0,degree_f=0,degree_t=0):
  """helper function to create a t/f polc with the given c00 coefficient,
  and with given order in t/f""";
  polc = meq.polc(zeros((degree_t+1, degree_f+1))*0.0);
  polc.coeff[0,0] = c00;
  return polc;

def tpolc (tdeg,c00=0.0):
  return Meq.Parm(create_polc(degree_f=0,degree_t=tdeg,c00=c00),
                  node_groups='Parm')

def _define_forest(ns):
 
  # create some MeqConstants
  BEAM_LM = [(0.048,-0.048)]
  l_beam,m_beam = BEAM_LM[0]
  ns.l_beam_c << Meq.Constant(l_beam)
  ns.m_beam_c << Meq.Constant(m_beam)

  solvable_list = []
  # create two MeqParms that have initial values of zero - see the tpolc
  # function above
  ns.beam_wt_re << tpolc(0)
  solvable_list.append(ns.beam_wt_re)
  ns.beam_wt_im << tpolc(0)
  solvable_list.append(ns.beam_wt_im)

  # now set up condeqs and solver that will be used to assign the contents of
  # the two MeqConstant nodes above to the MeqParm nodes
  condeq_list = []
  ns.condeq_wt_re << Meq.Condeq(children=(ns.l_beam_c, ns.beam_wt_re))
  condeq_list.append(ns.condeq_wt_re)
  ns.condeq_wt_im << Meq.Condeq(children=(ns.m_beam_c, ns.beam_wt_im))
  condeq_list.append(ns.condeq_wt_im)

  ns.solver<<Meq.Solver(children=condeq_list,num_iter=3,epsilon=1e-4,solvable=solvable_list)
  # put the above solver first in your MeqReqSeq node, and it will prime your MeqParms
  # for further use elsewhere in your tree