convert_equations: Convert equations notation

In dsem: Dynamic Structural Equation Models

Convert equations notation

Description

Converts equations to arrow-and-lag notation expected by dsem

Usage

convert_equations(equations)

Arguments

equations

Specification for time-series structural equation model structure including lagged or simultaneous effects. See Details section in convert_equations for more description

Details

The function modifies code copied from package sem under licence GPL (>= 2) with permission from John Fox.

For specifyEquations, each input line is either a regression equation or the specification of a variance or covariance. Regression equations are of the form y = par1x1 + par2x2 + ... + park*xk where y and the xs are variables in the model (either observed or latent), and the pars are parameters. If a parameter is given as a numeric value (e.g., 1) then it is treated as fixed. Note that no error variable is included in the equation; error variances are specified via either the covs argument, via V(y) = par (see immediately below), or are added automatically to the model when, as by default, endog.variances=TRUE. A regression equation may be split over more than one input by breaking at a +, so that + is either the last non-blank character on a line or the first non-blank character on the subsequent line.

Variances are specified in the form V(var) = par and covariances in the form C(var1, var2) = par, where the vars are variables (observed or unobserved) in the model. The symbols V and C may be in either lower- or upper-case. If par is a numeric value (e.g., 1) then it is treated as fixed. In conformity with the RAM model, a variance or covariance for an endogenous variable in the model is an error variance or covariance.

To set a start value for a free parameter, enclose the numeric start value in parentheses after the parameter name, as parameter(value).

dsem documentation built on Sept. 16, 2025, 9:10 a.m.