# Mass constraints for ApproxFun BVP system solver

**URL:** https://discourse.julialang.org/t/mass-constraints-for-approxfun-bvp-system-solver/82257
**Category:** Modelling & Simulations
**Tags:** approxfun
**Created:** [June 5, 2022, 3:29am UTC](https://discourse.julialang.org/t/mass-constraints-for-approxfun-bvp-system-solver/82257 "2022-06-05T03:29:22Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Jack\_hues](https://avatars.discourse-cdn.com/v4/letter/j/9fc348/32.png) [@Jack\_hues](https://discourse.julialang.org/u/Jack_hues)
#### Post date: [June 5, 2022, 3:29am UTC](https://discourse.julialang.org/t/mass-constraints-for-approxfun-bvp-system-solver/82257/1 "2022-06-05T03:29:22Z")

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Does ApproxFun currently have a way to solve BVPs with mass conservation? For example 0=u''+f(u,v) and 0=v''-f(u,v) with homogeneous Neumann boundary conditions or periodic boundary conditions. Namely, can I tell ApproxFun what the total mass is so that the linearization of this operator is invertible? Something like \int u+vdx=A.