Evaluate ODE Solution

Evaluate solution of a differential equation solver.

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)))
#>      [,1]     [,2]
#> [1,]  0.5 3.272267
#> [2,]  1.0 4.507677
#> [3,]  1.5 4.953259
#> [4,]  2.0 5.112068
#  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()