DGLOBAL

Bulk Data Entry

DGLOBAL – Input Data for Selecting the Global Search Option

Description

Defines input parameters required for the Global Search Option (GSO).

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
DGLOBAL	ID	NGROUP	NPOINT	SPMETH	NOUTDES	DESTOL
+		MAXSP	MAXSUCC	MAXWALL	MAXCPU
+	GROUP	SID1	NPOINT1	SPMETH1
+	GROUP	SID2	NPOINT2	SPMETH2
+	…	…

Field	Contents
ID	Each DGLOBAL card must have a unique ID. No default (Integer > 0)
NGROUP	Number of groups of design variables. See comment 1. Default = AUTO (Integer > 0, AUTO or blank)
NPOINT	Number of starting points for each group of design variables. See comment 1. Default = AUTO (Integer > 0, AUTO or blank)
SPMETH	Method used to generate the starting points. See comment 2. Default = OFFSET (EXTREME, OFFSET or blank)
NOUTDES	Number of unique designs to be saved. See comment 4. Default = ALL (Integer > 0, ALL or blank)
DESTOL	Unique design tolerance. See comment 4. Default = 1% (Real > 0.0 or blank)
MAXSP	Maximum number of starting points. See comment 5. Default = 20 (Integer > 0 or blank)
MAXSUCC	Maximum number of consecutive starting points without finding a unique design. See comment 5. Default = 10 (Integer > 0 or blank)
MAXWALL	Maximum amount of WALL time (in hours). See comment 5. Default = infinite (Real > 0.0 or blank)
MAXCPU	Maximum amount of CPU time (in hours). See comment 5. Default = infinite (Real > 0.0 or blank)
GROUP	Indicates that design variables grouping information is to follow. See comment 3.
SID#	Design variables SET identification number. No default (Integer > 0)
NPOINT#	Number of starting points for the current group of design variables. Default = AUTO (Integer > 0, AUTO or blank)
SPMETH#	Method used to generate the starting points for the current group of design variables. Default = AUTO (EXTREME, OFFSET, AUTO or blank)

Comments

Design variables are automatically organized in groups, and design variables within a given group are assigned the same relative starting points, such as their lower or upper bound. With the AUTO option, OptiStruct determines NGROUP and NPOINT so as to generate a reasonable and manageable number of starting points. Note that for small optimization problems, each design variable might be assigned its own group. By default, the number of groups is equal to the number of independent design variables with an upper limit of 10. For larger optimization problems, design variables are grouped together in order to consolidate the potential starting points. The values of NGROUP and NPOINT vary based on the model being solved. If the number of groups (NGROUP) is set too low, many design variables will be changed at the same time and variation in the optimum result is minimal, and therefore, does not serve the purpose of using the Global Search Option. If too many groups are defined, it may lead to unnecessary runs that converge to the same local optimum. The number of starting points is equal to (NPOINT)NGROUP, unless MAXSP is set to a very low value or MAXSUCC is attained (MAXWALL and MAXCPU can also affect the number of starting points).

2.	With the EXTREME option, the lower and upper bounds are included in the list of starting points; whereas with the OFFSET option, the lower and upper bounds are not considered as starting points. In both cases, the starting points are distributed evenly.

In situations where finer control is required, design variables can be grouped manually by creating DESVAR SETs. NPOINT# and SPMETH# can also be defined for individual groups. If those parameters are not defined for a specific group, they inherit their value from the generic NPOINT and SPMETH parameters.

The unique design tolerance DESTOL provides the threshold under which two designs are considered identical. It is measured as the average of the relative differences between the design variables at the last iteration. If such identical designs are found, the best occurrence is preserved and other results are discarded. Up to NOUTDES unique designs are saved in subdirectories named <filename_#s_#u>, where #s is the starting point and #u is the rank of the unique design.

5.	The global search option stops searching for optimal designs when any of the following criteria has been met:

•	the maximum number of starting points (MAXSP) has been reached

•	the maximum number of consecutive starting points without finding a unique design (MAXSUCC) has been reached

•	the maximum amount of WALL time (MAXWALL) has been reached or exceeded

•	the maximum amount of CPU time (MAXCPU) has been reached or exceeded

•	all possible starting points have been explored

6.	In general, it is recommended to run the global search option with the default parameters, except for the termination criteria.

7.	The DGLOBAL bulk data entry is referenced by the DGLOBAL command in the I/O section of the input data.