# Utility Function to Prepare Polynomial Fitted Edges of Trapezoid

Source:`R/trapezoid_utilities.R`

`polynomial_coefficients.Rd`

Called by `optram_wetdry_coefficients`

to prepare second order polynomial curve along trapezoid edges
Calculates six coefficients: intercept (alpha) of both wet and dry edges
and first and second order coefficients (beta), as in
\(STR = alpha + beta_1 * VI + beta_2 * VI^2\)
and updates the edges data.frame with these polynomila values fitted values

## Value

df, data.frame, the trapezoid line edge points with fitted values added for both wet and dry edges

## Note

Three CSV files are saved:

the regressions coefficients,

the trapezoid edge points

RMSE of the fitted curve

## Examples

```
if (FALSE) { # \dontrun{
df <- read.csv(system.file("extdata", "trapezoid_edges.csv",
package = "rOPTRAM"))
output_dir <- tempdir()
coeffs <- rOPTRAM::polynomial_coefficients(df, output_dir)
coeffs
} # }
```