# Error convergence bug

**URL:** https://community.freefem.org/t/error-convergence-bug/1360
**Category:** General Discussion
**Created:** [November 29, 2021, 1:24am UTC](https://community.freefem.org/t/error-convergence-bug/1360 "2021-11-29T01:24:25Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![Qianrui](https://avatars.discourse-cdn.com/v4/letter/q/9fc348/32.png) [@Qianrui](https://community.freefem.org/u/Qianrui)
#### Post date: [November 29, 2021, 1:24am UTC](https://community.freefem.org/t/error-convergence-bug/1360/1 "2021-11-29T01:24:25Z")

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Hi,To solve an equation, the order of error convergence is 2 in theory, but the result of numerical simulation is 1 in theory. Why ?

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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: [November 30, 2021, 1:54pm UTC](https://community.freefem.org/t/error-convergence-bug/1360/2 "2021-11-30T13:54:48Z")

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because you make a bug !!!

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### Author: ![Qianrui](https://avatars.discourse-cdn.com/v4/letter/q/9fc348/32.png) [@Qianrui](https://community.freefem.org/u/Qianrui)
#### Post date: [December 1, 2021, 7:32am UTC](https://community.freefem.org/t/error-convergence-bug/1360/3 "2021-12-01T07:32:31Z")

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Thanks. After simplification, the equation can reach the second order in time, but when a certain term is added, it becomes the first order. Why?

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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: [December 4, 2021, 3:36pm UTC](https://community.freefem.org/t/error-convergence-bug/1360/4 "2021-12-04T15:36:30Z")

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I think , They are an over bug.