v4l2_fract

v4l2_fract是Linux内核中的一个结构体，用于表示视频帧率。v4l2_fract结构体包含两个成员变量，分别是numerator（分子）和denominator（分母）。通过这两个成员变量，可以表示视频的帧率。

具体来说，numerator表示每秒钟的帧数，denominator表示每帧的时间间隔。例如，如果numerator为30，denominator为1，则表示视频的帧率为30帧每秒。

v4l2_fract结构体在视频设备驱动程序中经常被使用，用于设置和获取视频设备的帧率信息。通过设置v4l2_fract结构体的值，可以调整视频的帧率，从而满足不同应用场景的需求。

相关问题

train_dataset = MRIDataset(fixed_train_set, acceleration=acc, center_fraction=cen_fract,

我可以回答这个问题。train_dataset是一个MRIDataset类的实例，它使用fixed_train_set作为数据集，同时使用加速度(acc)和中心分数(cen_fract)进行加速MRI图像的重建。

全球等经纬度投影，分辨率为0.25度，WRF模拟em_real中namelist.input配置样例

下面是一个WRF模拟em_real中namelist.input的样例，其中包含了全球等经纬度投影和0.25度的分辨率配置：

&time_control
 run_days                            = 0,
 run_hours                           = 12,
 run_minutes                         = 0,
 run_seconds                         = 0,
 start_year                          = 2021, 2021, 2021,
 start_month                         = 07,   07,   07,
 start_day                           = 13,   14,   15,
 start_hour                          = 12,   12,   12,
 start_minute                        = 00,   00,   00,
 start_second                        = 00,   00,   00,
 end_year                            = 2021, 2021, 2021,
 end_month                           = 07,   07,   07,
 end_day                             = 14,   15,   16,
 end_hour                            = 00,   00,   00,
 end_minute                          = 00,   00,   00,
 end_second                          = 00,   00,   00,
 interval_seconds                    = 21600
 input_from_file                     = .true.,.true.,.true.,
 history_interval                    = 60,  60,  60,
 frames_per_outfile                  = 1,   1,   1,
 restart                             = .false.,
 restart_interval                    = 5000,
 io_form_history                     = 2
 io_form_restart                     = 2
 io_form_input                       = 2
 io_form_boundary                    = 2
 debug_level                         = 0
/

&domains
 time_step                           = 300,
 time_step_fract_num                 = 0,
 time_step_fract_den                 = 1,
 max_dom                             = 1,
 e_we                                = 1440,
 e_sn                                = 721,
 e_vert                              = 31,
 p_top_requested                     = 5000,
 num_metgrid_levels                  = 32,
 num_metgrid_soil_levels             = 4,
 dx                                  = 0.25,
 dy                                  = 0.25,
 grid_id                             = 1,
 parent_id                           = 0,
 i_parent_start                      = 1,
 j_parent_start                      = 1,
 parent_grid_ratio                   = 1,
 parent_time_step_ratio              = 1,
 feedback                            = 1,
 smooth_option                       = 0
/

&physics
 mp_physics                          = 3,
 ra_lw_physics                       = 1,
 ra_sw_physics                       = 1,
 radt                                = 30,
 sf_sfclay_physics                   = 1,
 sf_surface_physics                  = 2,
 bl_pbl_physics                      = 1,
 bldt                                = 0,
 cu_physics                          = 1,
 cudt                                = 5,
 isfflx                              = 1,
 ifsnow                              = 0,
 icloud                              = 1,
 surface_input_source                = 1,
 num_soil_layers                     = 4,
 sf_urban_physics                    = 0,
 maxiens                             = 1,
 maxens                              = 3,
 maxens2                             = 3,
 maxens3                             = 16,
 ensdim                              = 144,
/

&fdda
/

&dynamics
 w_damping                           = 0,
 diff_opt                            = 1,
 km_opt                              = 4,
 diff_6th_opt                        = 0,
 diff_6th_factor                     = 0.12,
 base_temp                           = 290.
 damp_opt                            = 0,
 zdamp                               = 5000., 5000., 5000.,
 dampcoef                            = 0.2,   0.2,   0.2,
 khdif                               = 0,     0,     0,
 kvdif                               = 0,     0,     0,
 non_hydrostatic                     = .true.,
 moist_adv_opt                       = 1,
 scalar_adv_opt                      = 1,
/

&bdy_control
 spec_bdy_width                      = 5,
 spec_zone                           = 1,
 relax_zone                          = 4,
 specified                           = .true., .false.,.false.,
 nested                              = .false.,.true., .true.,
/

&grib2
/

&namelist_quilt
 nio_tasks_per_group = 0,
 nio_groups = 1,
/

注意，这只是一个样例，具体配置可能需要根据你的模拟需求进行调整。