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    %% Specify the Innovation Distribution
% The property |Distribution| in a model stores the distribution name (and
% degrees of freedom for the _t_ distribution). The data type of
% |Distribution| is a |struct| array. For a Gaussian innovation
% distribution, the data structure has only one field: |Name|. For a
% Student's _t_ distribution, the data structure must have two fields:
% 
% * |Name|, with value |'t'|
% * |DoF|, with a scalar value larger than two (|NaN| is the default
% value)
%%
% If the innovation distribution is Gaussian, you do not need to assign a
% value to |Distribution|. |arima| creates the required data structure.
%%
% To illustrate, consider specifying an MA(2) model with an iid Gaussian
% innovation process:

% Copyright 2015 The MathWorks, Inc.

Mdl = arima(0,0,2)
%%
% The model output shows that |Distribution| is a |struct| array with one
% field, |Name|, with the value |'Gaussian'|.
%%
% When specifying a Student's _t_ innovation distribution, you can specify
% the distribution with either unknown or known degrees of freedom. If the
% degrees of freedom are unknown, you can simply assign |Distribution| the
% value |'t'|. By default, the property |Distribution| has a data structure
% with field |Name| equal to |'t'|, and field |DoF| equal to |NaN|. When
% you input the model to |estimate|, the degrees of freedom are estimated
% along with any other unknown model parameters.
%%
% For example, specify an MA(2) model with an iid Student's
% _t_ innovation distribution, with unknown degrees of freedom:
Mdl = arima('MALags',1:2,'Distribution','t')
%%
% The output shows that |Distribution| is a data structure with two fields.
% Field |Name| has the value |'t'|, and field |DoF| has the value |NaN|.
%%
% If the degrees of freedom are known, and you want to set an equality
% constraint, assign a |struct| array to |Distribution| with fields |Name|
% and |DoF|. In this case, if the model is input to |estimate|, the degrees
% of freedom won't be estimated (the equality constraint is upheld).
%%
% Specify an MA(2) model with an iid Student's _t_ innovation process with
% eight degrees of freedom:
Mdl = arima('MALags',1:2,'Distribution',struct('Name','t','DoF',8))
%%
% The output shows the specified innovation distribution.