# Problem of calculating error order **URL:** https://community.freefem.org/t/problem-of-calculating-error-order/3727 **Category:** General Discussion **Created:** [February 4, 2025, 4:43pm UTC](https://community.freefem.org/t/problem-of-calculating-error-order/3727 "2025-02-04T16:43:49Z") **Posts on this page:** 1 **Page:** 1
### Author: ![zezi-yang](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/zezi-yang/32/2944_2.png) [@zezi-yang](https://community.freefem.org/u/zezi-yang) #### Post date: [February 4, 2025, 4:43pm UTC](https://community.freefem.org/t/problem-of-calculating-error-order/3727/1 "2025-02-04T16:43:49Z")
Hello everyone, I encountered a weird situation when calculating the error order of Time-dependent Ginzburg-Landau(TDGL) equation. In order to calculate this equation, I use BDF1 discretization in time, P1 element in space for Psi, and BDM1Ortho element for A which means A belongs to hcurl space. ![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/b/ba25d2a099181519abdd1e6cca07e8354e16325f.png) Here is my weak form, and due to the influence of the boundary term, there is no boundary integral in the weak form ![QQ20250205-002830](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/f/fdbdc28aee2166a49b5cabb4bfa391bfbb234438.png) In calculation, because of the discretization method I selected, theoretically, the time error order should be 1 and the space error order should be 2. And I set the relationship between dt and h as dt=h^2. And the weird part came. When I calculated T=1 or T=1/8, the result was wrong, but when T=10, the error order was right. I don’t know what caused it. What I hope is that the correct result will appear when T is small. Here is my code : [GL(bdf1).edp](https://community.freefem.org/uploads/short-url/13ZLqnrn23QTxy5Md35YEdHUyjO.edp) (4.1 KB) Because of the computer, I didn’t set h to be small, but I don’t think it’s the key of the problem If you have any suggestions, I would be very grateful! 🥹