Description Usage Arguments Details Value Note See Also Examples

Detect events in solutions of a differential equation.

1 |

`x` |
vector of (time) points at which the differential equation has been solved. |

`y` |
values of the function(s) that have been computed for the given (time) points. |

`yv` |
point or numeric vector at which the solution is wanted. |

`idx` |
index of functions whose vales shall be returned. |

Determines when (in `x`

coordinates) the `idx`

-th solution
function will take on the value `yv`

.

The interpolation is linear for the moment. For points outside the
`x`

interval `NA`

is returned.

A (time) point `x0`

at which the event happens.

The interpolation is linear only for the moment.

1 2 3 4 5 6 7 8 9 10 11 | ```
## Damped pendulum: y'' = -0.3 y' - sin(y)
# y1 = y, y2 = y': y1' = y2, y2' = -0.3*y2 - sin(y1)
f <- function(t, y) {
dy1 <- y[2]
dy2 <- -0.3*y[2] - sin(y[1])
return(c(dy1, dy2))
}
sol <- rk4sys(f, 0, 10, c(pi/2, 0), 100)
deeve(sol$x, sol$y[,1]) # y1 = 0 : elongation in [sec]
# [1] 2.073507 5.414753 8.650250
# matplot(sol$x, sol$y); grid()
``` |

```
[1] 2.073507 5.414753 8.650250
```

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