[kk415]

Hello Foamers,


I have a list of cells in which I don't want to run my cell loop, how can I subtract this list from the cellList ?

[kk415]

I have written this loop but I feel there is scope of optimizing this.



int nNew=0;
int check=0;
forAll(newMesh.cells(),cellI)
{
forAll(unrefCells,I)
{
if(cellI == unrefCells[I])
{
check=1;
break;
}
}
if(check == 0)
{
nNew++;
newCells.resize(nNew,cellI);
}
check=0;
}

[raumpolizei]

Hey,
here are some ideas that may improve perfomance :
1. Don't use a function call in your forAll macro. Maybe the compiler will optimize it but it is possible that the function gets called multiple times (when range checking is performed).

const cellList& newMeshCells = newMesh.cells();
forAll(newMeshCells,cellI)
// instead of
// forAll(newMesh.cells(),cellI)

I don't know if forAll works for const fields, otherwise make a for loop out of it.
2. The optimization of your second for loop depends on what data is in newMeshCells and also whether the data is sorted or not. A Foam::List<T> should be fine. You could for example take advantage of a sorted container and perform a binary search on newMeshCells. This will enhance performance especially if the size of your container is big.

#include<algorithm>
...
forAll(unRefCells,I)
{
  bool found=std::binary_search(newMeshCells.begin(),newMeshCells.end(),I);
  if(found)
  {
    break;
    ...
  }
  ...
}

What you definitely should do is check the algorithm section on cppreference.com (you'll find more info on binary search and a few helpful algorithms).
Good luck with your task.
Cheers
RP

[olesen]

Originally Posted by kk415

I have written this loop but I feel there is scope of optimizing this.
int nNew=0;
int check=0;
forAll(newMesh.cells(),cellI)
{
forAll(unrefCells,I)
{
if(cellI == unrefCells[I])
{
check=1;
break;
}
}
if(check == 0)
{
nNew++;
newCells.resize(nNew,cellI);
}
check=0;
}

I can't really follow what you are trying to do, but it is certainly more efficient and easier if you try to work at a higher level. For example (don't really know if this is what you are trying)

bitSet  unrefCells = ...;  // Some selection coming from somewhere (your input?)

// Those were the cells you want to ignore, so we need the opposite.

labelList newCells;

if (unrefCells.none())
{
    // Nothing ignored - take all cells
    newCells = identity(newMesh.nCells());
}
else if (unrefCells.all())
{
    //  All ignored - we don't have any new cells?
}
else
{
    // Some ignored - get the other ones
    unrefCells.resize(newMesh.nCells());   // extra safety

    unrefCells.flip();
    newCells = unrefCells.toc();  // or sortedToc() - same thing
    unrefCells.flip();   // return to original state
 }

There isn't a simple and efficient way of getting the "unselected" values from the bitSet at the moment.

If it suits your requirement, you might also get some use out of subsetting too.

bitSet  unrefCells = ...;  // Some selection coming from somewhere (your input?)

scalarField inputValues = ...;

// Subset of the 'off' values:
scalarField values = subset(unrefCell, inputValue, true);

In any case, you were quite right to have a bad feeling about all of the resize() operations within a loop.


Cheers,
/mark