Developers Meeting Notes 6/1/12

This week we discussed the following topics:

1. Tim Brick is implementing analytical gradient calculations in the backend. To prepare for this new feature, we discussed how to revise the mxOptions() to specify which type of gradient calculation is performed.

The "Calculate Hessian" option is preserved from the existing interface, and enables or disables the Hessian calculation. The default value is "Yes".

The "Hessian Type" option dictates what type of Hessian calculation is performed:

• "Analytic" calculates the analytical Hessian and marks missing cells with NA values.
• "Numeric" calculates the Hessian numerically.
• "Both" will return two Hessian matrices, one from each calculation.
• "Blended" calculates the analytical Hessian and fills in any missing cells using the numerical Hessian.

The new default value will be "Blended". In OpenMx 1.2 and earlier, the effective default value was "Numeric". The option "Both" can be helpful in debugging.

2. Ryne's helper function standardizeRAM.R was moved into the summary() function for single model RAM objective functions. The script standardizeRAM.R will be copied into the wiki for advanced users.