# Having a Jump BC for a continuous element type

**URL:** <https://community.freefem.org/t/having-a-jump-bc-for-a-continuous-element-type/1673>\
**Category:** General Discussion\
**Created:** [April 15, 2022, 7:38pm UTC](https://community.freefem.org/t/having-a-jump-bc-for-a-continuous-element-type/1673 "2022-04-15T19:38:56Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mahdi](https://avatars.discourse-cdn.com/v4/letter/m/e9c0ed/32.png) [@mahdi](https://community.freefem.org/u/mahdi)\
**Post date:** [April 15, 2022, 7:38pm UTC](https://community.freefem.org/t/having-a-jump-bc-for-a-continuous-element-type/1673/1 "2022-04-15T19:38:56Z")

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Dear colleagues;  
Is it possible to have a jump over an edge for a continuous element type? Based on my smattering, it should work for p0, p1dc, p2dc, …  
However, the example in the document has done it for a p1 element.

 ![Screenshot from 2022-04-15 12-32-50](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/0/0ffcbcb6a978b1fcc49c4c6123d2e7f73a354e62.png)

I have a line over which I want to jump my **P2-element type** variable for a constant value. Is such a thing possible?

 ![Untitled](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/6/605949fedac09d0600b384503932cbd84a9aeacf.png)

Any idea is much appreciated!

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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:** [April 18, 2022, 3:03pm UTC](https://community.freefem.org/t/having-a-jump-bc-for-a-continuous-element-type/1673/2 "2022-04-18T15:03:34Z")

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You can use DG formulation, and add constraint jump(phi) = c on some internal boundary,  
Sorry, You have , I have no time to write the correct formulation but I am sure it is possible.

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**Author:** ![mahdi](https://avatars.discourse-cdn.com/v4/letter/m/e9c0ed/32.png) [@mahdi](https://community.freefem.org/u/mahdi)\
**Post date:** [April 28, 2022, 8:20am UTC](https://community.freefem.org/t/having-a-jump-bc-for-a-continuous-element-type/1673/3 "2022-04-28T08:20:19Z")

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Dear Professor Hecht;  
I couldn’t find any source mentioning how to write it:

My problem is jumping over an internal boundary like:  
 ![Screenshot from 2022-04-23 22-06-26](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/d/d467b976c66f2b55300a84ff5860deda7326bc5b.png)  
For the equation:  
r\nabla^2 \psi =r \nabla \cdot q- \nabla \cdot \mu   
To have a jumep equal to 2_pi I have written as:  
solve Mahdi( ψ , v )= int2d(Th)( r_(dx( ψ )\*dx(v) + dy( ψ )_dy(v)) ) + int2d(Th)( ( μ x-r_ qx )_dx(v) + ( μ y-r_ qy )_dy(v) )  
+  
intalledges(Th)((label==1)_ v \* (2 \*pi)\*jump( ψ ));

And it is not working…

Could you please kindly refer me to how to use the jump function? I couldn’t find it with the existing documentation.  
Thanks so much.