I'm trying to calculate some volumes using R. Imagine I have the following data:

```
h=seq(from=663,by=0.1,length.out=11); #Vector of reference heights
Ap=0.25; #Discretization area
z=c(NA,NA,NA,663.05,663.13,663.25,663.33,663.45,663.67,663.84,663.9,664.39,NA,NA,NA); #Elevation of every element in the surface
```

What I want is to generate a vector returning a Riemann sum, computing the product `Ap*(h-z)`

for every element in `z<h`

.

Does anyone know how this can be achieved using R?

I have tried using `sapply()`

, but I haven't been successful so far.

Thank you in advance for any help!