D1: Computing each element of the function c_weight_1
In Opt5PL: Optimal Designs for the 5-Parameter Logistic Model

This function computes each element of the vector function c_weight_1 which is the first derivative of the c-optimality criterion with respect to the model parameters.

1	D1(T, x, xl, inv, p, order)

`T`	A numeric vector. Model parameter values
`x`	A numeric. ith dose level for a given design
`xl`	A numeric. last dose level for a given design
`inv`	A numeric matrix. Inverse of the information matrix
`p`	A numeric. Define EDp
`order`	numeric. The number of model paraemters