Prev Next Index-> contents reference index search external Up-> CppAD ADFun optimize CppAD-> Install Introduction AD ADFun preprocessor multi_thread utility ipopt_solve Example speed Appendix ADFun-> record_adfun drivers Forward Reverse sparsity_pattern sparse_derivative optimize abs_normal FunCheck check_for_nan optimize-> optimize_forward_active.cpp optimize_reverse_active.cpp optimize_compare_op.cpp optimize_print_for.cpp optimize_conditional_skip.cpp optimize_nest_conditional.cpp optimize_cumulative_sum.cpp Headings-> Syntax Purpose f options ---..no_conditional_skip ---..no_compare_op ---..no_print_for_op Examples Efficiency Speed Testing Atomic Functions ---..rev_sparse_jac ---..nan Checking Optimization


Syntax
f.optimize()  f.optimize(options) 
Purpose
The operation sequence corresponding to an ADFun object can be very large and involve many operations; see the size functions in seq_property . The f.optimize procedure reduces the number of operations, and thereby the time and the memory, required to compute function and derivative values.

f
The object f has prototype       ADFun<Base> f 
options
This argument has prototype       const std::string& options  The default for options is the empty string. If it is present, it must consist of one or more of the options below separated by a single space character.

no_conditional_skip
The optimize function can create conditional skip operators to improve the speed of conditional expressions; see optimize . If the sub-string no_conditional_skip appears in options , conditional skip operations are not be generated. This may make the optimize routine use significantly less memory and take less time to optimize f . If conditional skip operations are generated, it may save a significant amount of time when using f for forward or reverse mode calculations; see number_skip .

no_compare_op
If the sub-string no_compare_op appears in options , comparison operators will be removed from the optimized function. These operators are necessary for the compare_change functions to be meaningful. On the other hand, they are not necessary, and take extra time, when the compare_change functions are not used.

no_print_for_op
If the sub-string no_compare_op appears in options , PrintFor operations will be removed form the optimized function. These operators are useful for reporting problems evaluating derivatives at independent variable values different from those used to record a function.

Examples
 forward_active.cpp Example Optimization and Forward Activity Analysis reverse_active.cpp Example Optimization and Reverse Activity Analysis compare_op.cpp Example Optimization and Comparison Operators print_for_op.cpp Example Optimization and Print Forward Operators conditional_skip.cpp Example Optimization and Conditional Expressions nest_conditional.cpp Example Optimization and Nested Conditional Expressions cumulative_sum.cpp Example Optimization and Cumulative Sum Operations

Efficiency
If a zero order forward calculation is done during the construction of f , it will require more memory and time than required after the optimization procedure. In addition, it will need to be redone. For this reason, it is more efficient to use       ADFun<Base> f;      f.Dependent(x, y);      f.optimize();  instead of       ADFun<Base> f(x, y)      f.optimize();  See the discussion about sequence constructors .

Speed Testing
You can run the CppAD speed tests and see the corresponding changes in number of variables and execution time. Note that there is an interaction between using optimize and onetape . If onetape is true and optimize is true, the optimized tape will be reused many times. If onetape is false and optimize is true, the tape will be re-optimized for each test.

Atomic Functions
There are some subtitle issue with optimized atomic functions $v = g(u)$:

rev_sparse_jac
The atomic_rev_sparse_jac function is be used to determine which components of u affect the dependent variables of f . For each atomic operation, the current atomic_sparsity setting is used to determine if pack_sparsity_enum, bool_sparsity_enum, or set_sparsity_enum is used to determine dependency relations between argument and result variables.

nan
If u[i] does not affect the value of the dependent variables for f , the value of u[i] is set to nan .

Checking Optimization
If NDEBUG is not defined, and f.size_order() is greater than zero, a forward_zero calculation is done using the optimized version of f and the results are checked to see that they are the same as before. If they are not the same, the ErrorHandler is called with a known error message related to f.optimize() .