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UDF: Given coordinates, How to identify the cell?

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Old   August 9, 2012, 17:35
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Bradley J
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Hello All.
I have tried running this code for a 2D axissymetric case and recieved this error:

..\..\src\find.c(14) : error C2100: illegal indirection
..\..\src\find.c(14) : error C2440: '=' : cannot convert from 'int' to 'CX_Cell_Id'

this is line 14
cx_cell=*CX_Find_Cell_With_Point(pt);

code:
#include"udf.h"
#include"cxndsearch.h"
DEFINE_ON_DEMAND(find_cell)
{
#if !RP_HOST
Domain *d;
cell_t c;
Thread *t;
CX_Cell_Id cx_cell;
real NV_VEC(pt);
real c_centroid[ND_ND];
NV_D(pt,=,0.009995,0.000175,0.0);
CX_Start_ND_Point_Search();
cx_cell=*CX_Find_Cell_With_Point(pt);
CX_End_ND_Point_Search();
c=RP_CELL(&cx_cell);
t=RP_THREAD(&cx_cell);
C_CENTROID(c_centroid,c,t);
Message(
"coordinate of the specified point: x=%g,y=%g\n",pt[0],pt[1]);
Message(
"coordinate of the cell found: x=%g,y=%g\n",c_centroid[0],c_centroid[1]);
#endif
}
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Old   August 24, 2012, 17:30
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Paul H
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I'm having compilation issues too- tried to compile on windows and linux, the compiler complains about the the same line:

cx_cell=*CX_Find_Cell_With_Point(pt);

Has anyone gotten this work? Any details on fluent version, environment?

This seems like an extremely useful function.
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Old   October 28, 2013, 09:13
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Mat
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Dear all,

I know is a bit a late, but it can be usefull for futur users.

I suppose the function "CX_Find_Cell_With_Point" was available with the previous versions of Fluent (Actually, I used it with succes in Fluent 6.0, but it doesnt work with Fluent 14.5).

If you want the same functionality, you can use the function "SV_locate_point" with the actual version of Fluent :

Code:
  ...
  cell_t c;
  Thread *t;
  CX_Cell_Id *cx_cell;
  float pos[3];
  ...
  SV_locate_point(pos, cx_cell);
  c = cx_cell->ct.c; 
  t = cx_cell->ct.t;
  ...
Unfortunately, it does not seem to work in parallel (only for serial calculation).
In the parallel case, I don't see another solution than doing the loop among the cell yourself, and communicate between the nodes.

Best,

Mat
mm.abdollahzadeh and wond like this.
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Old   June 24, 2014, 14:21
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Garvit Goel
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Quote:
Originally Posted by md5encrypted View Post
I found this code (source: http://www.cfluid.com/bbs/viewthread...able&tid=76550)

Code:
cell_t c;
Thread *t;
CX_Cell_Id cx_cell;
real NV_VEC(pt);
real c_centroid[ND_ND];

NV_D(pt, =, 1,1,1);  //coordinate of your specified location,it must be in the domain coordinate range
CX_Start_ND_Point_Search();
cx_cell=*CX_Find_Cell_With_Point(pt);
CX_End_ND_Point_Search();
c=RP_CELL(&cx_cell);  //the right cell number
t = RP_THREAD(&cx_cell);  //  the thread

C_CENTROID(c_centroid,c,t);
Message0("coordinate of the specified point: x=%g,y=%g,z=%g\n",pt[0],pt[1],pt[2]);
Message0("coordinate of the cell found: x=%g,y=%g,z=%g,T=%g\n",c_centroid[0],c_centroid[1],c_centroid[2],C_T(c,t));
It works, but if requested point located outside mesh, CX_Find_Cell_With_Point returns NULL, and therefore causes access violation (dereferencing NULL).


[off] I know I'm late with answer, but hope it will be useful [/off]
I am getting the error -
invalid type argument of unary * (have int)
and warnings that -
implicit declaration of function
CX_Start_ND_Point_Search
CX_Find_Cell_With_Point
CX_End_ND_Point_Search
Thanks a lot
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Old   October 16, 2016, 02:32
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the source code of the higher version is seem to be changed.
the 'search' is a struct type whose variables are not illustrated yet.


Quote:
Originally Posted by Vitaly View Post
Hello,

In my cxndsearch.h file, the input arguments are different:

FLUENT_EXPORT CX_Cell_Id *CX_Find_Cell_With_Point(ND_Search *, double v[3], double time);

I have no idea what "time" means, but I set it to 0.0 and it worked.
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Old   December 11, 2018, 07:58
Default What should be put between brackets
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What should be put between brackets in CX statemetns in a real code?

CX_Start_ND_Point_Search(ND_Search *, cxboolean do_domain, int t_id);
CX_Find_Cell_With_Point(ND_Search *, float v[3]);
CX_End_ND_Point_Search(ND_Search *)

I would need a short example with the CX_... loop inside a code and CX_...(?) content.

Last edited by jacek; December 12, 2018 at 05:48.
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Old   August 15, 2022, 06:54
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George Pichurov
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Quote:
Originally Posted by Jura
;152697
Hello,

you ought to use macro C_CENTROID(x,c,c_thread) I would expect enclose it in cell looping macro begin_c_loop(c, c_thread) - end_c_loop(...) -> then you can check if x=x[0],y=x[1],z=x[2] matches your coordinates via if-function.
Well, almost certainly it will not match. Even if your point is microns from the cell centre, machine arithmetic will still give a false. I suppose we need a way to find if a a point lies within the cell boundaries. Trying to pinpoint the cell centre is useless.
You can loop to find the cell centre closest to the desired point. I have done that. But, in parallel computation (and resp. compilation) each partition assigned to a process loops through that loop and finds it own point, closest to the desired coordinate, but belonging to its partition. So I end up with n cells (where n is the number of processes=partitions) that are not necessary close to the desired coordinate. So we need one of two things:
1. Either find a way if a coordinate lies within a cell entity (within the boundaries of a cell), or
2. Find a way to loop by a host process and not by compute processes. However, the ID will be duplicate (for example cell number lets say 140 will exist in all partitions of a parallel run)
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