Yinjian Zhao

@RemiLehe @ax3l Now, the loaded external field (1st plot) looks different from the provided external field (2nd plot). I'm stuck at debugging. Maybe you guys can help when reviewing this...

> What is the reason that this requires creating new multifabs, `Efield_fp_external` and `Bfield_fp_external` instead of using `E/Bfield_fp`, `E/Bfield_aux` and `E/Bfield_cp` as is currently done with input like `Ex_external_grid_function(x,y,z)`? Basically...

Record a working test! [constant_B.txt](https://github.com/ECP-WarpX/WarpX/files/9004856/constant_B.txt) This (Jupyter Notebook) python script generates a constant Bz field and other zero fields into txt files. Then, this version of the PR will read...

Record a working test in RZ! [constant_B_rz.txt](https://github.com/ECP-WarpX/WarpX/files/9221660/constant_B_rz.txt) This (Jupyter Notebook) python script generates a constant Bz field and other zero fields into txt files. Then, this version of the PR...

Record a working test in XZ! [constant_B_xz.txt](https://github.com/ECP-WarpX/WarpX/files/9222130/constant_B_xz.txt) This (Jupyter Notebook) python script generates a constant By field and other zero fields into txt files. Then, this version of the PR...

Record a working test in 1D! [constant_E_z.txt](https://github.com/ECP-WarpX/WarpX/files/9222406/constant_E_z.txt) This (Jupyter Notebook) python script generates a constant Ez field and other zero fields into txt files. Then, this version of the PR...

Tested a more complicated 3D scenario: magnetic mirror effect. 1. A 2D RZ magnetic mirror field is generated by the [FEMM](https://www.femm.info/wiki/HomePage) software. The field is shown as this figure. ...

Now, the mirror 3D test is applied using OpenPMD. [openpmd_create.txt](https://github.com/ECP-WarpX/WarpX/files/9271468/openpmd_create.txt) reads the previous `B*.txt` and `E*.txt` txt data files and converts them into OpenPMD format file `openpmd_data.h5`. [B0.txt](https://github.com/ECP-WarpX/WarpX/files/9271499/B0.txt) [B1.txt](https://github.com/ECP-WarpX/WarpX/files/9271501/B1.txt) [B2.txt](https://github.com/ECP-WarpX/WarpX/files/9271502/B2.txt)...

Currently, I'm trying to use this piece of code to do the job, but I'm a little bit confused about the indexing of phi and Ex. The simulation has nx=500,...

Well, because I don't quite know if the above is doing correctly, (noticed I was using staggered grid, but switched to collocated grid now), and the simulation speed drops a...