(xi, yi)
| 208 | return ui * dt_ds, vi * dt_ds |
| 209 | |
| 210 | def g(xi, yi): |
| 211 | dt_ds = 1.0 / self.value_at(self.speed, xi, yi) |
| 212 | ui = self.value_at(self.u, xi, yi) |
| 213 | vi = self.value_at(self.v, xi, yi) |
| 214 | return -ui * dt_ds, -vi * dt_ds |
| 215 | |
| 216 | def check(xi, yi): |
| 217 | return (0 <= xi < len(self.x) - 1) and (0 <= yi < len(self.y) - 1) |