# Error using dxx(u) with meshL

**URL:** <https://community.freefem.org/t/error-using-dxx-u-with-meshl/1448>\
**Category:** General Discussion\
**Created:** [January 23, 2022, 2:26pm UTC](https://community.freefem.org/t/error-using-dxx-u-with-meshl/1448 "2022-01-23T14:26:52Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![renordgren](https://avatars.discourse-cdn.com/v4/letter/r/a698b9/32.png) [@renordgren](https://community.freefem.org/u/renordgren)\
**Post date:** [January 23, 2022, 2:26pm UTC](https://community.freefem.org/t/error-using-dxx-u-with-meshl/1448/1 "2022-01-23T14:26:52Z")

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When I use the dxx(u) operator on a meshL function u, I get the following error:

Assertion fail : (0)  
line :245, in file …/femlib/P012\_3dCurve.cpp

My code:  
load “msh3” // needed for using meshL command  
int nx = 10;  
real L=1.0;  
meshL Th=segment(nx,[L\*x,0,0]);  
fespace Vh(Th,P2);

Vh u,v;

u=cos(2_pi_x/L);  
v=dx(u);  
v=dxx(u);

I am running the latest version: – FreeFem++ v4.1 (Sat, Nov 13, 2021 7:40:01 PM - git v4.10) on Windows 11. The line immediately before v=dx(u); works just fine and I have no issues with it.

Cheers!  
Rich

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [January 25, 2022, 3:56pm UTC](https://community.freefem.org/t/error-using-dxx-u-with-meshl/1448/2 "2022-01-25T15:56:54Z")

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I will correct in version [correct error un dxx P2 meshL case. · FreeFem/FreeFem-sources@bddf3c4 · GitHub](https://github.com/FreeFem/FreeFem-sources/commit/bddf3c4ef8ab595657e2c1980c9684932cc56537), Thanks

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [January 28, 2022, 4:04pm UTC](https://community.freefem.org/t/error-using-dxx-u-with-meshl/1448/3 "2022-01-28T16:04:07Z")

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