LineValueSampler: VectorPostProcessor in PostProcessor

[TFdvd]

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Question

Hello MOOSE community!
I'm intrested in the behaviour of LineValueSampler. In particular, the latter is a VectorPostProcessor and I get a .csv for each iteration. Is it possible to pass LineValueSampler from a VectorPostProcessor to a PostProcessor so that I can manipulate its behaviour to obtain a single .csv? Specifically, LineValueSampler in VectorPostProcessor returns me a .csv with a number of results = num_points (requested parameter) . My idea is to save this dataset, but to manipulate it in the PostProcessor area to get a single value of my interest.
Do you have any suggestions for following this path? Maybe this is a silly question, but I don't have much experience.
Thanks for your time and patience :)

[GiudGiud]

Hello

All the postprocessors get lumped into the same CSV file by default.
However you can create a cutom CSV output and use the 'show' parameter to select which postprocessors to print there.

You can retrieve the vector values of of a VPP in a custom postprocessor using

getVectorPostprocessorValue("name of VPP", "which vector")

this return a reference, you should save it in an attribute of your custom PP

[GiudGiud]

What error do you get?

[TFdvd]

I don't get an error. The results are not coherent and I think that my procedure is wrong when I pass [variable] from VPP to PP. Maybe, passing the vector "[variable]" in the right way, I will solve the problem.

[GiudGiud]

Can you report here the print out of the vector in the VPP and in the PP?

[TFdvd]

Yes, sure!
A generic .csv of my VPP is:

C_along_vertical_0005_.xlsx

The file above treats the i-th iteration. On the previous file, that comes from VPP, I'm only interested on the entire vector c (1st column) that I want to export on the PP in order to catch one only value of my interest.

The result of my PP for all iteration in the single value of my interest is:

c_neck.xlsx

As you can see, the repeted value 8.8931816251424e-323 in c_neck.xlsx file is not coherent and maybe VPP and PP are not comunicate well from the previous .C and .i that I attached. Thanks for your patience @GiudGiud

[GiudGiud]

 8.8931816251424e-323

means an unitialized value in C++

what is happening is that nothing ever calls computeValue().
You need to do this

void 
NeckValue::execute()
{
  computeValue();
}

or move the code in computeValue into execute

[TFdvd]

Hello @GiudGiud!
I really want to thank you for your help, my custom PP works almost 100%. I have solved almost all the problems except for one detail that doesn't add up. From the results I attach below you can see that at the first iteration 0.2 I get 3.22 e-320 while at iteration 0.5 I get 4.42, which is the result I need to get in 0.2. In other words, I get the results of the current iteration at the next iteration.

Time | c
0 | 0
0.2 | 3.56e-321
0.5 | 4.84
0.95 | 6.06
. | .
. | .
. | ...... and so on

I have tried indexing the for loop in various ways without getting a solution. I attach the .C below. Do you have any suggestions or notice anything that might explain this tendency? The explanation I have found is that perhaps the PP runs the loop before the VPP and so at the current iteration the PP finds no value from the VPP, while at the next iteration the PP finds data from the VPP which is still at the previous iteration. I don't know if this makes sense, but I would like to know your point of view and how I could solve this last detail. Thanks again for your help @GiudGiud !

#include "NeckValue.h"

registerMooseObject("ParrotApp", NeckValue);

InputParameters
NeckValue::validParams()
{
InputParameters params = GeneralPostprocessor::validParams();
params.addRequiredParam("threshold", "Seconda variabile");
params.addRequiredParam("tolerance", "Terza variabile");
params.addRequiredParam("vpp", "The name of the VectorPostprocessor to pull the data from."); //new
params.addRequiredParamstd::string("vector_name","The name of the vector to use from the VectorPostprocessor"); //new
params.addParam<std::vector>("c_var", std::vector{}, "Vector of real values used in computation.");
return params;
}

NeckValue::NeckValue(
const InputParameters &parameters)
: GeneralPostprocessor(parameters),
_threshold(getParam("threshold")),
_tolerance(getParam("tolerance")),
_c_var(getParam<std::vector>("c_var")) //virgola in più

{}

void
NeckValue::initialize()
{

_c_var = getParam<std::vector>("c_var");

}

void
NeckValue::execute()
{
computeValue();
}

Real NeckValue::computeValue() {

const VectorPostprocessorValue & _c_var = getVectorPostprocessorValueByName(getParam("vpp"),getParamstd::string("vector_name"));

for (unsigned int i = 0; i < _c_var.size(); i++)

{
if (std::abs(_c_var[i] - _threshold) < _tolerance)
{

  _value = _c_var[i]; 

[ ]

  _index = i;

  _true_neck = (_index * 0.303); 

  break; 
}  

}

return _true_neck; 

}

PostprocessorValue NeckValue::getValue() const
{
return _true_neck;

}

[GiudGiud]

ok so what must be happening is that the postprocessor is executed before the VPP

so to fix that, use execution_order_groups (a parameter for both PPs, VPPs and UOs), and set the PP to be executed after the VPP

[TFdvd]

Perhaps I have not understood your point of view.
The VPP has to be executed first in order to provide the data to the PP afterwards.
If it is a matter of using execution_order_groups anyway, could you explain how to do that? Thanks in advance

[GiudGiud]

in the VPP set
execution_order_group = 0
in the PP set
execution_order_group = 1

that should work

[TFdvd]

You're right!! Thank a lot @GiudGiud