Evaluate ODE Solution
Evaluate solution of a differential equation solver.
deval(x, y, xp, idx = NULL)
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. |
Determines where the points xp lie within the vector x
and interpolates linearly.
An length(xp)-by-length(idx) matrix of values at points
xp.
The interpolation is linear only for the moment.
## 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()
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