mxOption is used to set, clear, or query an option (given in the key argument)
in the back-end optimizer. Valid option keys are listed below.Use value = NULL to remove an existing option. Leaving value blank will return 
the current value of the option specified by key.
To reset all options to their default values, use reset = TRUE. 
When reset = TRUE, key and value are ignored. 
If the model argument is set to NULL, the default optimizer option (i.e
those applying to all models by default) will be set.
To see the defaults, use getOption('mxOptions').
Before the model is submitted to the back-end, all keys and values are converted into
strings using the as.character function.
The maximum number of major iterations (the option  Major iterations) 
for optimization for NPSOL  can be specified either by using a 
numeric value (such as 50, 1000, etc) or by specifying a user-defined function.
The user-defined function should accept two arguments as input, the number of 
parameters and the number of constraints, and return a numeric value as output.
OpenMx options
rcl{
Number of Threads 	i          	the number of processor cores to use. Use detectCores()
 to find how many are available. 
Calculate Hessian 	[Yes | No]       	calculate the Hessian explicitly after optimization. 
Standard Errors   	[Yes | No]       	return standard error estimates from the explicitly calculate hessian. 
Default optimizer 	[NPSOL | SLSQP] 	the gradient descent optimizer to use 
Number of Threads 	[0|1|2|...|10|...] 	number of threads used for optimization.  This is how parallelism works. Default value of 0 uses detectCores() - 1. 
Feasibility tolerance 	r 	the maximum acceptable absolute violations in linear and nonlinear constraints. 
Optimality tolerance 	r 	the maximum acceptable difference in fit. 
Gradient algorithm 	see list 	finite difference method, either 'forward' or 'central'. 
}
SLSQP is our new, experimental optimizer.
NPSOL-specific options
rcl{
Nolist                		this option suppresses printing of the options 
Print level           	i 	the value of i controls the amount of printout produced by the major iterations 
Minor print level     	i 	the value of i controls the amount of printout produced by the minor iterations 
Print file            	i 	for i > 0 a full log is sent to the file with logical unit number i. 
Summary file          	i 	for i > 0 a brief log will be output to file i. 
Function precision    	r 	a measure of accuracy with which f and c can be computed. 
Infinite bound size   	r 	if r > 0 defines the "infinite" bound bigbnd. 
Major iterations      	i or a function 	the maximum number of major iterations before termination. 
Verify level          	[-1:3 | Yes | No]     	see NPSOL manual. 
Line search tolerance 	r    	controls the accuracy with which a step is taken. 
Derivative level      	[0-3]      	see NPSOL manual. 
Hessian               	[Yes | No] 	return the Hessian (Yes) or the transformed Hessian (No). 
}
Checkpointing options
rcl{
Always Checkpoint    	[Yes | No]    	whether to checkpoint all models during optimization.
Checkpoint Directory 	path       	the directory into which checkpoint files are written. 
Checkpoint Prefix    	string     	the string prefix to add to all checkpoint filenames. 
Checkpoint Fullpath  	path       	overrides the directory and prefix (useful to output to /dev/fd/2) 
Checkpoint Units     	see list   	the type of units for checkpointing: 'minutes', 'iterations', or 'evaluations'. 
Checkpoint Count     	i    	the number of units between checkpoint intervals. 
}
Model transformation options
rcl{
Error Checking           	[Yes | No] 	whether model consistency checks are performed in the OpenMx front-end 
No Sort Data             		character vector of model names for which FIML data sorting is not performed 
RAM Inverse Optimization 	[Yes | No] 	whether to enable solve(I - A) optimization 
RAM Max Depth            	i    	the maximum depth to be used when solve(I - A) optimization is enabled 
}
Multivariate normal integration parameters
rcl{
mvnMaxPointsA 	i 	base number of integration points 
mvnMaxPointsB 	i 	number of integration points per row 
mvnMaxPointsC 	i 	number of integration points per rows^2 
mvnAbsEps     	i 	absolute tolerance 
mvnRelEps     	i 	relative tolerance 
}