# The definition mismatch of the double layer operator

**URL:** https://bempp.discourse.group/t/the-definition-mismatch-of-the-double-layer-operator/96
**Category:** Bempp
**Created:** [15 September 2021 11:38 UTC](https://bempp.discourse.group/t/the-definition-mismatch-of-the-double-layer-operator/96 "2021-09-15T11:38:18Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![LCheng](https://avatars.discourse-cdn.com/v4/letter/l/9fc348/32.png) [@LCheng](https://bempp.discourse.group/u/LCheng)
#### Post date: [15 September 2021 11:38 UTC](https://bempp.discourse.group/t/the-definition-mismatch-of-the-double-layer-operator/96/1 "2021-09-15T11:38:18Z")

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Hello,

I found that the definition of the double layer on the “Bempp book” [Bempp book](http://bempp.com/handbook/api/boundary_operators.html) is not matched with the publication(E. V. Wout, P. Gelat, T. Betcke and S. Arridge, 138(5), JASA, 2015). I have checked the Bempp code, and found that it might be consistent with the later definition from JASA paper. The two definitions are parsed below. I hope my finding is useful for other users.

 ![image](https://global.discourse-cdn.com/free1/uploads/bempp/original/1X/b98fbebef425a86cad4624289e0075d8215f5729.png)  
**[Bempp book]**

![image](https://global.discourse-cdn.com/free1/uploads/bempp/original/1X/8f20d27ed2f748099adc7abffd38a56ad3dcc5d2.png)  
**JASA Paper**

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### Author: ![timo](https://yyz2.discourse-cdn.com/free1/user_avatar/bempp.discourse.group/timo/32/7_2.png) [@timo](https://bempp.discourse.group/u/timo)
#### Post date: [15 September 2021 20:07 UTC](https://bempp.discourse.group/t/the-definition-mismatch-of-the-double-layer-operator/96/2 "2021-09-15T20:07:32Z")

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Hi, the definition from the Bempp book is consistent with the implementation in the code.

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### Author: ![LCheng](https://avatars.discourse-cdn.com/v4/letter/l/9fc348/32.png) [@LCheng](https://bempp.discourse.group/u/LCheng)
#### Post date: [16 September 2021 01:24 UTC](https://bempp.discourse.group/t/the-definition-mismatch-of-the-double-layer-operator/96/3 "2021-09-16T01:24:57Z")

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Hi, Timo, thanks. I just found that my description is wrong. Your answer is correct.

Best wishes,  
Long