Dakota Reference Manual
Version 6.2
LargeScale Engineering Optimization and Uncertainty Analysis

Specifies the parameter set to be iterated by a particular method.
This keyword is related to the topics:
Alias: none
Argument(s): none
Required/Optional  Description of Group  Dakota Keyword  Dakota Keyword Description  

Optional  id_variables  Name the variables block; helpful when there are multiple  
Optional  active  Set the active variables view a method will see  
Optional (Choose One)  Group 1  mixed  Maintain continuous/discrete variable distinction  
relaxed  Allow treatment of discrete variables as continuous  
Optional  continuous_design  Continuous design variables; each defined by a real interval  
Optional  discrete_design_range  Discrete design variables; each defined by an integer interval  
Optional  discrete_design_set  Setvalued discrete design variables  
Optional  normal_uncertain  Aleatory uncertain variable  normal (Gaussian)  
Optional  lognormal_uncertain  Aleatory uncertain variable  lognormal  
Optional  uniform_uncertain  Aleatory uncertain variable  uniform  
Optional  loguniform_uncertain  Aleatory uncertain variable  loguniform  
Optional  triangular_uncertain  Aleatory uncertain variable  triangular  
Optional  exponential_uncertain  Aleatory uncertain variable  exponential  
Optional  beta_uncertain  Aleatory uncertain variable  beta  
Optional  gamma_uncertain  Aleatory uncertain variable  gamma  
Optional  gumbel_uncertain  Aleatory uncertain variable  gumbel  
Optional  frechet_uncertain  Aleatory uncertain variable  Frechet  
Optional  weibull_uncertain  Aleatory uncertain variable  Weibull  
Optional  histogram_bin_uncertain  Aleatory uncertain variable  continuous histogram  
Optional  poisson_uncertain  Aleatory uncertain discrete variable  Poisson  
Optional  binomial_uncertain  Aleatory uncertain discrete variable  binomial  
Optional  negative_binomial_uncertain  Aleatory uncertain discrete variable  negative binomial  
Optional  geometric_uncertain  Aleatory uncertain discrete variable  geometric  
Optional  hypergeometric_uncertain  Aleatory uncertain discrete variable  hypergeometric  
Optional  histogram_point_uncertain  Aleatory uncertain variable  discrete histogram  
Optional  uncertain_correlation_matrix  Correlation among aleatory uncertain variables  
Optional  continuous_interval_uncertain  Epistemic uncertain variable  values from one or more continuous intervals  
Optional  discrete_interval_uncertain  Epistemic uncertain variable  values from one or more discrete intervals  
Optional  discrete_uncertain_set  Setvalued discrete uncertain variables  
Optional  continuous_state  Continuous state variables  
Optional  discrete_state_range  Discrete state variables; each defined by an integer interval  
Optional  discrete_state_set  Setvalued discrete state variables 
The variables
specification in a Dakota input file specifies the parameter set to be iterated by a particular method.
In the case of
To accommodate these different studies, Dakota supports different:
Use the variables page to browse the available variables by type and domain.
Variable Types
initial_value
is used as the only value for the state variable for all other methods, unless active
state
is invoked.Variable Domains
Continuous variables are defined by bounds. Discrete variables can be defined in one of three ways, which are discussed on the page discrete_variables.
Ordering of Variables
The ordering of variables is important, and a consistent ordering is employed throughout the Dakota software. The ordering is shown in dakota.input.summary and can be summarized as:
Ordering of variable types below this granularity (e.g., from normal to histogram bin within aleatory uncertain  continuous ) is defined somewhat arbitrarily, but is enforced consistently throughout the code.
Active Variables
The reason variable types exist is that methods have the capability to treat variable types differently. All methods have default behavior that determines which variable types are "active" and will be assigned values by the method. For example, optimization methods will only vary the design variables  by default.
The default behavior should be described on each method page, or on topics pages that relate to classes of methods. In addition, the default behavior can be modified using the active keyword.
Several examples follow. In the first example, two continuous design variables are specified:
variables, continuous_design = 2 initial_point 0.9 1.1 upper_bounds 5.8 2.9 lower_bounds 0.5 2.9 descriptors 'radius' 'location'
In the next example, defaults are employed. In this case, initial_point
will default to a vector of 0
. values, upper_bounds
will default to vector values of DBL_MAX
(the maximum number representable in double precision for a particular platform, as defined in the platform's float.h
C header file), lower_bounds
will default to a vector of DBL_MAX
values, and descriptors
will default to a vector of 'cdv_i'
strings, where i
ranges from one to two:
variables, continuous_design = 2
In the following example, the syntax for a normallognormal distribution is shown. One normal and one lognormal uncertain variable are completely specified by their means and standard deviations. In addition, the dependence structure between the two variables is specified using the uncertain_correlation_matrix
.
variables, normal_uncertain = 1 means = 1.0 std_deviations = 1.0 descriptors = 'TF1n' lognormal_uncertain = 1 means = 2.0 std_deviations = 0.5 descriptors = 'TF2ln' uncertain_correlation_matrix = 1.0 0.2 0.2 1.0
An example of the syntax for a state variables specification follows:
variables, continuous_state = 1 initial_state 4.0 lower_bounds 0.0 upper_bounds 8.0 descriptors 'CS1' discrete_state_range = 1 initial_state 104 lower_bounds 100 upper_bounds 110 descriptors 'DS1'
And in a more advanced example, a variables specification containing a set identifier, continuous and discrete design variables, normal and uniform uncertain variables, and continuous and discrete state variables is shown:
variables, id_variables = 'V1' continuous_design = 2 initial_point 0.9 1.1 upper_bounds 5.8 2.9 lower_bounds 0.5 2.9 descriptors 'radius' 'location' discrete_design_range = 1 initial_point 2 upper_bounds 1 lower_bounds 3 descriptors 'material' normal_uncertain = 2 means = 248.89, 593.33 std_deviations = 12.4, 29.7 descriptors = 'TF1n' 'TF2n' uniform_uncertain = 2 lower_bounds = 199.3, 474.63 upper_bounds = 298.5, 712. descriptors = 'TF1u' 'TF2u' continuous_state = 2 initial_state = 1.e4 1.e6 descriptors = 'EPSIT1' 'EPSIT2' discrete_state_set_int = 1 initial_state = 100 set_values = 100 212 375 descriptors = 'load_case'