# Product of two integrals on a boundary

**URL:** https://community.freefem.org/t/product-of-two-integrals-on-a-boundary/4205
**Category:** General Discussion
**Created:** [January 28, 2026, 3:35pm UTC](https://community.freefem.org/t/product-of-two-integrals-on-a-boundary/4205 "2026-01-28T15:35:02Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![jna1g18](https://avatars.discourse-cdn.com/v4/letter/j/77aa72/32.png) [@jna1g18](https://community.freefem.org/u/jna1g18)
#### Post date: [January 28, 2026, 3:35pm UTC](https://community.freefem.org/t/product-of-two-integrals-on-a-boundary/4205/1 "2026-01-28T15:35:02Z")

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Hi all, is there a standard way to incorporate a product of two integrals over a 1D boundary into the weak formulation? One integral contains the unknown being solved for and the other contains a test function. For example, is it possible to have a term like the following in the weak form:

 ![Screenshot from 2026-01-28 15-33-19](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/e/e288473524e457ce7f681321f9466845ad7cc400.png)

Naively trying to include this into the weak formulation causes an error and I’m wondering if there’s a standard method that I’m not aware of. Let me know if you require further information. Thanks!