R: Evaluate ODE Solution

deval {pracma} | R Documentation

## Evaluate ODE Solution

### Description

Evaluate solution of a differential equation solver.

### Usage

    deval(x, y, xp, idx = NULL)

### Arguments

`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.
`xp` | point or numeric vector at which the solution is wanted; must be sorted.
`idx` | index of functions whose vales shall be returned.

### Details

Determines where the points `xp` lie within the vector `x` and interpolates linearly.

### Value

An `length(xp)`-by-`length(idx)` matrix of values at points `xp`.

### Note

The interpolation is linear only for the moment.

### See Also

`deeve`

### Examples

    ##  Free fall:  v' = -g - cw abs(v)^1.1,  cw = 1.6 drag coefficien
    f <- function(t, y) -9.81 + 1.6*abs(y)^1.1
    sol <- rk4(f, 0, 10, 0, 100)
    # speed after 0.5, 1, 1.5, 2 seconds
    cbind(c(0.5,1,1.5,2), -deval(sol$x, sol$y, c(0.5, 1, 1.5, 2)))
    #  0.5  3.272267  m/s
    #  1.0  4.507677
    #  1.5  4.953259
    #  2.0  5.112068
    # plot(sol$x, -sol$y, type="l", col="blue"); grid()

[Package pracma version 2.0.4 Index]