prob_true: Probability of Selecting the True Model.
In penplaqr/penplaqr:

Given coefficient estimates from a set of simulations, prob_true calculates the proportion of simulations that selected the true model exactly.

1	prob_true(model_coefficients, true_coefficients, threshold)

`model_coefficients`	a vector or matrix of coefficient estimates. If a matrix, then the coefficients should vary by row and the simulations should vary by column.
`true_coefficients`	a vector of indices of the true non-zero coefficients.
`threshold`	a scalar value below which a coefficient should be considered equal to zero.