Paulo G.P. - 7 months ago 51

R Question

I'm having some problems with integration function in R. I'm trying to plot the integral vo but it seems I'm not doing correctly.

`t <- seq(0, 0.04, 0.0001)`

vi <- function(x) {5 * sin(2 * pi * 50 * x)}

vo <- function(x) {integrate(vi, lower=0, upper=x)$value}

test_vect = Vectorize(vo, vectorize.args='x')

plot(t, vo(t)) # should be a cosine wave

plot(t, vi(t)) # sine wave

`vo`

`test_vect`

`vo`

Answer

You are already there. Just use `plot(t, test_vect(t))`

. You can't use `vo`

, as `integrate`

is not a vectorized function. There is no problem to evaluate a single point like `vo(0.002)`

, but you can not feed it a vector by `vo(t)`

. This is why we want `Vectorize(vo)(t)`

.

You said that `test_vect`

is not giving the right plot. Sure? We can analytically compute the integral:

```
v <- function (x) (1-cos(100*pi*x)) / (20*pi)
```

Then let's compare:

```
sum(abs(v(t) - test_vect(t)))
# [1] 2.136499e-15
```

They are the same!