Optimization Overview
The Local Optimization (or simply, "Optimization") feature provided by OpticStudio is quite powerful, and is capable of improving lens designs given a reasonable starting point and a set of variable parameters. Variables can be curvatures, thicknesses, glasses, conics, parameter data, extra data, and any of the numeric multi-configuration data. OpticStudio uses either an actively damped least squares or an orthogonal descent algorithm. The algorithms are capable of optimizing a merit function composed of weighted target values; these target values are called "operands". There are several different default merit functions, described in a subsequent section. These merit functions can be changed easily using the Merit Function Editor. For details on this procedure see "Modifying the merit function".
Optimization requires three steps: 1) a reasonable system which can be traced, 2) specification of the variables, and 3) a merit function. A reasonable system is a rather loose concept which means that poorly conceived designs are not likely to be transformed into exceptional designs by the optimization algorithm (although there are exceptions). The variables, and there must be at least one for the optimization algorithm to be able to make any progress, are specified on the various editors, as described in the next section.
The algorithm used by the optimization feature described in this chapter is designed to find the "local" minimum of the specified merit function. However, OpticStudio also has the capability to search for a "global" minimum of the merit function. The global minimum is the lowest possible value for the merit function, and if the merit function is selected appropriately, this implies the best possible solution to the problem. The global optimization feature is not for novice users, and is not appropriate for interactive designing. For details see "Global Optimization".
About cycles and systems
During optimization, the "Number of Cycles" is displayed on the dialogs for both local and global optimizers, while the "Number of Systems" is only shown on the dialog of the global optimizers (Global Search and Hammer). This is because while the Number of Systems provides an indication of how much of solution space has been covered during global optimization (a process that will otherwise run indefinitely), this number is not a meaningful metric for analyzing the performance of the local optimization. An increase in the Number of Systems by one simply means that OpticStudio has calculated the merit function for one combination of proposed variables, while an increase in the Number of Cycles by one means that the optimizer has evaluated the merit function for several systems and found a path to move towards the local minima in solution space. The number of system evaluations included in one cycle is related to the number of variables; as more variables are defined, more systems will need to be included in each optimization cycle, thus increasing the optimization time.
Next:
- Selecting optimization variables
- Modifying the merit function
- Notes on Operand Weights
- Understanding Boundary Operands
- Performing an optimization
- Defining complex operands
- Optimizing zoom and multi-configuration lenses
- Optimizing Tolerance Sensitivity (optimization overview)
- User Defined Operands (optimization overview)
- Suggestions for optimizing
- The Global Optimum
- Sequential Optimization
- Global Optimization