FMPMonotonicityCheck: Utility function for checking FMP monotonicity

In fungible: Psychometric Functions from the Waller Lab

Utility function for checking FMP monotonicity

Description

Utility function for checking whether candidate FMP coefficients yield a monotonically increasing polynomial.

Usage

FMPMonotonicityCheck(b, lower = -20, upper = 20, PLOT = FALSE)

Arguments

b	A vector of 8 polynomial coefficients (b) for m(\theta)=b_0 + b_1 \theta + b_2 \theta^2 + b_3 \theta^3 + b_4 \theta^4 + b_5 \theta^5 + b_6 \theta^6 + b_7 \theta^7.
lower, upper	\theta bounds for monotonicity check.
PLOT	Logical (default = FALSE). If PLOT = TRUE the function will plot the original polynomial function for \theta between lower and upper.

Value

increasing	Logical indicating whether function is monotonically increasing.
minDeriv	Minimum value of the derivative for the polynomial.
minTheta	Value of \theta at derivative minimum.

Author(s)

Niels Waller

Examples

## A set of candidate coefficients for an FMP model.
## These coefficients fail the test and thus
## should not be used with genFMPdata to generate
## item response data that are consistent with an 
## FMP model.
 b <- c(1.21, 1.87, -1.02, 0.18, 0.18, 0, 0, 0)
 FMPMonotonicityCheck(b)

fungible documentation built on May 29, 2024, 8:28 a.m.