Error in a simple mesh generation from FreeFem++?

General Discussion
1

Hi there,
I’m trying to generate a mesh using FreeFem++ and the docker image (because packaging is broken right now on my OS).

While it works online using https://freefem.org/tryit (see the attached screenshot), it does not when using the docker container:

root@7a0b8b6a2f5e:/data# /usr/freefem/bin/FreeFem++ l.edp
-- FreeFem++ v4.7 (Fri Sep  4 03:15:07 UTC 2020 - git no git)
 Load: lg_fem lg_mesh lg_mesh3 eigenvalue
    1 : real clockwise = 10;
    2 : real anticlockwise = -10;
    3 : border b351434140(t=0., 1.){x=4.8266172+t*(4.8266342-4.8266172); y=45.747651+t*(45.7476708-45.747651); label=35143414;}
    4 : border b351434141(t=0., 1.){x=4.8266342+t*(4.8266534-4.8266342); y=45.7476708+t*(45.7476931-45.7476708); label=35143414;}
    5 : border b351434142(t=0., 1.){x=4.8266534+t*(4.8266557-4.8266534); y=45.7476931+t*(45.7476957-45.7476931); label=35143414;}
    6 : border b351434143(t=0., 1.){x=4.8266557+t*(4.826679-4.8266557); y=45.7476957+t*(45.747723-45.7476957); label=35143414;}
    7 : border b351434144(t=0., 1.){x=4.826679+t*(4.8266808-4.826679); y=45.747723+t*(45.747725-45.747723); label=35143414;}
    8 : border b351434145(t=0., 1.){x=4.8266808+t*(4.8266936-4.8266808); y=45.747725+t*(45.74774-45.747725); label=35143414;}
    9 : border b351434146(t=0., 1.){x=4.8266936+t*(4.8267194-4.8266936); y=45.74774+t*(45.74777-45.74774); label=35143414;}
   10 : border b351434147(t=0., 1.){x=4.8267194+t*(4.826749-4.8267194); y=45.74777+t*(45.7478045-45.74777); label=35143414;}
   11 : border b351434148(t=0., 1.){x=4.826749+t*(4.8267831-4.826749); y=45.7478045+t*(45.7478441-45.7478045); label=35143414;}
   12 : border b351434149(t=0., 1.){x=4.8267831+t*(4.8268092-4.8267831); y=45.7478441+t*(45.7478745-45.7478441); label=35143414;}
   13 : border b3514341410(t=0., 1.){x=4.8268092+t*(4.8268337-4.8268092); y=45.7478745+t*(45.747903-45.7478745); label=35143414;}
   14 : border b3514341411(t=0., 1.){x=4.8268337+t*(4.8268566-4.8268337); y=45.747903+t*(45.7479297-45.747903); label=35143414;}
   15 : border b3514341412(t=0., 1.){x=4.8268566+t*(4.824565-4.8268566); y=45.7479297+t*(45.7488883-45.7479297); label=35143414;}
   16 : border b3514341413(t=0., 1.){x=4.824565+t*(4.8245356-4.824565); y=45.7488883+t*(45.748854-45.7488883); label=35143414;}
   17 : border b3514341414(t=0., 1.){x=4.8245356+t*(4.8245137-4.8245356); y=45.748854+t*(45.7488285-45.748854); label=35143414;}
   18 : border b3514341415(t=0., 1.){x=4.8245137+t*(4.8244847-4.8245137); y=45.7488285+t*(45.7487947-45.7488285); label=35143414;}
   19 : border b3514341416(t=0., 1.){x=4.8244847+t*(4.8244537-4.8244847); y=45.7487947+t*(45.7487587-45.7487947); label=35143414;}
   20 : border b3514341417(t=0., 1.){x=4.8244537+t*(4.8244221-4.8244537); y=45.7487587+t*(45.7487219-45.7487587); label=35143414;}
   21 : border b3514341418(t=0., 1.){x=4.8244221+t*(4.8243962-4.8244221); y=45.7487219+t*(45.7486917-45.7487219); label=35143414;}
   22 : border b3514341419(t=0., 1.){x=4.8243962+t*(4.8243684-4.8243962); y=45.7486917+t*(45.7486594-45.7486917); label=35143414;}
   23 : border b3514341420(t=0., 1.){x=4.8243684+t*(4.8243342-4.8243684); y=45.7486594+t*(45.7486238-45.7486594); label=35143414;}
   24 : border b3514341421(t=0., 1.){x=4.8243342+t*(4.8243213-4.8243342); y=45.7486238+t*(45.7486046-45.7486238); label=35143414;}
   25 : border b3514341422(t=0., 1.){x=4.8243213+t*(4.8243059-4.8243213); y=45.7486046+t*(45.7485867-45.7486046); label=35143414;}
   26 : border b3514341423(t=0., 1.){x=4.8243059+t*(4.8242759-4.8243059); y=45.7485867+t*(45.7485517-45.7485867); label=35143414;}
   27 : border b3514341424(t=0., 1.){x=4.8242759+t*(4.8242416-4.8242759); y=45.7485517+t*(45.7485132-45.7485517); label=35143414;}
   28 : border b3514341425(t=0., 1.){x=4.8242416+t*(4.8242196-4.8242416); y=45.7485132+t*(45.7484886-45.7485132); label=35143414;}
   29 : border b3514341426(t=0., 1.){x=4.8242196+t*(4.824185-4.8242196); y=45.7484886+t*(45.7484498-45.7484886); label=35143414;}
   30 : border b3514341427(t=0., 1.){x=4.824185+t*(4.8241644-4.824185); y=45.7484498+t*(45.7484219-45.7484498); label=35143414;}
   31 : border b3514341428(t=0., 1.){x=4.8241644+t*(4.8252637-4.8241644); y=45.7484219+t*(45.747962-45.7484219); label=35143414;}
   32 : border b3514341429(t=0., 1.){x=4.8252637+t*(4.8253519-4.8252637); y=45.747962+t*(45.7479253-45.747962); label=35143414;}
   33 : border b3514341430(t=0., 1.){x=4.8253519+t*(4.826456-4.8253519); y=45.7479253+t*(45.7474634-45.7479253); label=35143414;}
   34 : border b3514341431(t=0., 1.){x=4.826456+t*(4.8264849-4.826456); y=45.7474634+t*(45.7474941-45.7474634); label=35143414;}
   35 : border b3514341432(t=0., 1.){x=4.8264849+t*(4.8265158-4.8264849); y=45.7474941+t*(45.7475311-45.7474941); label=35143414;}
   36 : border b3514341433(t=0., 1.){x=4.8265158+t*(4.8265376-4.8265158); y=45.7475311+t*(45.7475572-45.7475311); label=35143414;}
   37 : border b3514341434(t=0., 1.){x=4.8265376+t*(4.8265704-4.8265376); y=45.7475572+t*(45.7475965-45.7475572); label=35143414;}
   38 : border b3514341435(t=0., 1.){x=4.8265704+t*(4.8266064-4.8265704); y=45.7475965+t*(45.7476384-45.7475965); label=35143414;}
   39 : border b3514341436(t=0., 1.){x=4.8266064+t*(4.8266172-4.8266064); y=45.7476384+t*(45.747651-45.7476384); label=35143414;}
   40 : mesh Th = buildmesh(b351434140(clockwise)+b351434141(clockwise)+b351434142(clockwise)+b351434143(clockwise)+b351434144(clockwise)+b351434145(clockwise)+b351434146(clockwise)+b351434147(clockwise)+b351434148(clockwise)+b351434149(clockwise)+b3514341410(clockwise)+b3514341411(clockwise)+b3514341412(clockwise)+b3514341413(clockwise)+b3514341414(clockwise)+b3514341415(clockwise)+b3514341416(clockwise)+b3514341417(clockwise)+b3514341418(clockwise)+b3514341419(clockwise)+b3514341420(clockwise)+b3514341421(clockwise)+b3514341422(clockwise)+b3514341423(clockwise)+b3514341424(clockwise)+b3514341425(clockwise)+b3514341426(clockwise)+b3514341427(clockwise)+b3514341428(clockwise)+b3514341429(clockwise)+b3514341430(clockwise)+b3514341431(clockwise)+b3514341432(clockwise)+b3514341433(clockwise)+b3514341434(clockwise)+b3514341435(clockwise)+b3514341436(clockwise));
   41 : plot(Th, ps="/data/Thwithouthole.eps");
   42 :  sizestack + 1024 =1864  ( 840 )

689 Problem: insert point 687([951477307,108774789],[4.82665,45.7477]{6.31137e-07,6.31137e-07,[1,0]})1122 tcvj = 0x7fabd1351148 0
([1024935376,194901279],[4.82686,45.7479]{0.00012596,0.00012596,[1,0]})([890714664,37610599],[4.82649,45.7475]{4.66524e-06,4.66524e-06,[1,0]})
([1024935376,194901279],[4.82686,45.7479]{0.00012596,0.00012596,[1,0]})([890714664,37610599],[4.82649,45.7475]{4.66524e-06,4.66524e-06,[1,0]})
 Fatal error in the mesh generator 1001
  current line = 3
Meshing error: Bamg
 number : 1001,
 catch Err bamg
Meshing error: Bamg
 number : 1001,
 err code 5 ,  mpirank 0

Any idea what’s the problem with this code? (Source is there: https://0x0.st/ilNu.txt )

Thanks,
Rémy

foo
foo7668×3495 2.99 MB

2

Another simpler example:

# cat l.edp
real clockwise = 100;
real anticlockwise = -100;
border building0poly0boundary0point0(t=0., 1.){x=4.8184454+t*(4.8183747-4.8184454); y=45.7308329+t*(45.7306317-45.7308329);}
border building0poly0boundary0point1(t=0., 1.){x=4.8183747+t*(4.818315-4.8183747); y=45.7306317+t*(45.7308105-45.7306317);}
border building0poly0boundary0point2(t=0., 1.){x=4.818315+t*(4.8183586-4.818315); y=45.7308105+t*(45.7309346-45.7308105);}
border building0poly0boundary0point3(t=0., 1.){x=4.8183586+t*(4.8183398-4.8183586); y=45.7309346+t*(45.7309856-45.7309346);}
border building0poly0boundary0point4(t=0., 1.){x=4.8183398+t*(4.8183639-4.8183398); y=45.7309856+t*(45.7310633-45.7309856);}
border building0poly0boundary0point5(t=0., 1.){x=4.8183639+t*(4.8184454-4.8183639); y=45.7310633+t*(45.7308329-45.7310633);}
mesh Th = buildmesh(building0poly0boundary0point0(anticlockwise)+building0poly0boundary0point1(anticlockwise)+building0poly0boundary0point2(anticlockwise)+building0poly0boundary0point3(anticlockwise)+building0poly0boundary0point4(anticlockwise)+building0poly0boundary0point5(anticlockwise));
plot(Th, ps="/data/Thwithouthole.eps");

And the result:

# FreeFem++ l.edp
-- FreeFem++ v4.7 (Fri Sep  4 03:15:07 UTC 2020 - git no git)
 Load: lg_fem lg_mesh lg_mesh3 eigenvalue
    1 : real clockwise = 100;
    2 : real anticlockwise = -100;
    3 : border building0poly0boundary0point0(t=0., 1.){x=4.8184454+t*(4.8183747-4.8184454); y=45.7308329+t*(45.7306317-45.7308329);}
    4 : border building0poly0boundary0point1(t=0., 1.){x=4.8183747+t*(4.818315-4.8183747); y=45.7306317+t*(45.7308105-45.7306317);}
    5 : border building0poly0boundary0point2(t=0., 1.){x=4.818315+t*(4.8183586-4.818315); y=45.7308105+t*(45.7309346-45.7308105);}
    6 : border building0poly0boundary0point3(t=0., 1.){x=4.8183586+t*(4.8183398-4.8183586); y=45.7309346+t*(45.7309856-45.7309346);}
    7 : border building0poly0boundary0point4(t=0., 1.){x=4.8183398+t*(4.8183639-4.8183398); y=45.7309856+t*(45.7310633-45.7309856);}
    8 : border building0poly0boundary0point5(t=0., 1.){x=4.8183639+t*(4.8184454-4.8183639); y=45.7310633+t*(45.7308329-45.7310633);}
    9 : mesh Th = buildmesh(building0poly0boundary0point0(anticlockwise)+building0poly0boundary0point1(anticlockwise)+building0poly0boundary0point2(anticlockwise)+building0poly0boundary0point3(anticlockwise)+building0poly0boundary0point4(anticlockwise)+building0poly0boundary0point5(anticlockwise));
   10 : plot(Th, ps="/data/Thwithouthole.eps");
   11 :  sizestack + 1024 =1368  ( 344 )

8272 Problem: insert point 8206([93579005,784780268],[4.81835,45.731]{5.65531e-07,5.65531e-07,[1,0]})8300 tcvj = 0x7fa2db2ea348 0
([94800954,681052721],[4.81835,45.7309]{1.31536e-06,1.31536e-06,[1,0]})([93767014,786995666],[4.81835,45.731]{5.43548e-07,5.43548e-07,[1,0]})
([94800954,681052721],[4.81835,45.7309]{1.31536e-06,1.31536e-06,[1,0]})([93767014,786995666],[4.81835,45.731]{5.43548e-07,5.43548e-07,[1,0]})
 Fatal error in the mesh generator 1001
  current line = 3
Meshing error: Bamg
 number : 1001,
 catch Err bamg
Meshing error: Bamg
 number : 1001,
 err code 5 ,  mpirank 0

The figure as plotted by matplotlib:

Figure
Figure3836×2072 69.6 KB

3

This is due to machine epsilons in the definition of your borders. Weird that it does not happen on the online demo though…

4

Thanks,

I thought about that but I was expecting freefem to used arbitrary precision. Is there some way to the “epsilon” used for comparison between points ? What’s the number format used by FreeFem? IEEE754? Is double precision available?

The online implementation is probably using javascript, so, different implementation of the number representation…

5

Is double precision available?

It’s the only available precision.

The online implementation is probably using javascript

No, it’s using FreeFEM under the hood, just a different version.