# integrateTrapezoid: Trapezoidal Integration

Description Usage Arguments Value Bugs Author(s) Examples

### Description

Estimate the integral of one-dimensional function using the trapezoidal rule.

### Usage

 `1` ```integrateTrapezoid(x, y, type = c("A", "dA", "cA"), xmin, xmax) ```

### Arguments

 `x, y` vectors of x and y values. In the normal case, these vectors are both supplied, and of equal length. There are also two special cases. First, if `y` is missing, then `x` is taken to be `y`, and a new `x` is constructed as `seq_along(y)`. Second, if `length(x)` is 1 and `length(y)` exceeds 1, then `x` is replaced by `x*seq_along(y)`. `type` Flag indicating the desired return value (see “Value”). `xmin, xmax` Optional numbers indicating the range of the integration. These values may be used to restrict the range of integration, or to extend it; in either case, `approx` with `rule=2` is used to create new x and y vectors.

### Value

If `type="A"` (the default), a single value is returned, containing the estimate of the integral of `y=y(x)`. If `type="dA"`, a numeric vector of the same length as `x`, of which the first element is zer0, the second element is the integral between `x[1]` and `x[2]`, etc. If `type="cA"`, the result is the cumulative sum (as in `cumsum`) of the values that would be returned for `type="dA"`. See “Examples”.

### Bugs

There is no handling of `NA` values.

Dan Kelley

### Examples

 ``` 1 2 3 4 5 6 7 8 9 10``` ```x <- seq(0, 1, length.out=10) # try larger length.out to see if area approaches 2 y <- 2*x + 3*x^2 A <- integrateTrapezoid(x, y) dA <- integrateTrapezoid(x, y, "dA") cA <- integrateTrapezoid(x, y, "cA") print(A) print(sum(dA)) print(tail(cA, 1)) print(integrateTrapezoid(diff(x[1:2]), y)) print(integrateTrapezoid(y)) ```

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