MATLAB Examples

# Compare Generalized and Orthogonalized Impulse Response Functions

This example shows the differences between orthogonal and generalized impulse response functions using the three-dimensional VAR(2) model in docid:econ_ug.brz_lcd, p. 78. The variables in the model represent the quarterly rates of fixed investment, disposable income, and consumption expenditures of Germany. The estimated model is

where and . The estimated covariance matrix of the innovations is

The VAR(2) model contains a constant, but because the impulse response function is the derivative of with respect to , the constant does not affect the impulse response function.

Create a cell vector containing the autoregressive coefficient matrices, and a matrix for the innovations covariance matrix.

AR1 = [-0.320 0.146 0.961; 0.044 -0.153 0.289; -0.002 0.225 -0.264]; AR2 = [-0.161 0.115 0.934; 0.050 0.019 -0.010; 0.034 0.355 -0.022]; ar0 = {AR1 AR2}; InnovCov = [21.30 0.72 1.23; 0.72 1.37 0.61; 1.23 0.61 0.89]*1e-4; 

Plot and compute the orthogonalized impulse response function. Because no VMA coefficients exist, specify an empty array ([]) for the second input argument.

figure; armairf(ar0,[],'InnovCov',InnovCov); OrthoY = armairf(ar0,[],'InnovCov',InnovCov); 

The impulse responses seem to die out after nine periods. OrthoY is a 10-by-3-by-3 matrix of impulse responses. The rows correspond to periods, columns correspond to a variable, and pages correspond to the variable receiving the shock.

Plot and compute the generalized impulse response function. Display both sets of impulse responses.

figure; armairf(ar0,[],'InnovCov',InnovCov,'Method','generalized'); GenY = armairf(ar0,[],'InnovCov',InnovCov,'Method','generalized'); for j = 1:3 fprintf('Shock to Response %d',j) table(OrthoY(:,:,j),GenY(:,:,j),'VariableNames',{'Orthogonal',... 'Generalized'}) end 
Shock to Response 1 ans = 10x2 table Orthogonal Generalized _________________________________________ _________________________________________ 0.046152 0.0015601 0.0026651 0.046152 0.0015601 0.0026651 -0.01198 0.0025622 -0.00044488 -0.01198 0.0025622 -0.00044488 -0.00098179 0.0012629 0.0027823 -0.00098179 0.0012629 0.0027823 0.0049802 2.1799e-05 6.3661e-05 0.0049802 2.1799e-05 6.3661e-05 0.0013726 0.00018127 0.00033187 0.0013726 0.00018127 0.00033187 -0.00083369 0.00037736 0.00012609 -0.00083369 0.00037736 0.00012609 0.00055287 1.0779e-05 0.00015701 0.00055287 1.0779e-05 0.00015701 0.00027093 3.2276e-05 6.2713e-05 0.00027093 3.2276e-05 6.2713e-05 3.7154e-05 5.1385e-05 9.3341e-06 3.7154e-05 5.1385e-05 9.3341e-06 2.325e-05 1.0003e-05 2.8313e-05 2.325e-05 1.0003e-05 2.8313e-05 Shock to Response 2 ans = 10x2 table Orthogonal Generalized _________________________________________ _________________________________________ 0 0.0116 0.0049001 0.0061514 0.011705 0.0052116 0.0064026 -0.00035872 0.0013164 0.0047488 -1.4011e-05 0.0012454 0.0050746 0.00088845 0.0035692 0.0048985 0.0010489 0.0039082 0.0020934 0.001419 -0.00069114 0.0027385 0.0014093 -0.00067649 0.0014919 -8.9823e-05 0.00090697 0.0016616 -6.486e-05 0.00094311 -0.00043831 0.00048004 0.00032749 -0.00054552 0.00052606 0.00034138 0.0011216 6.5734e-05 2.1313e-05 0.0011853 6.6585e-05 4.205e-05 0.00010281 2.9385e-05 0.00015523 0.000138 3.3424e-05 0.0001622 -3.2553e-05 0.00010201 2.6429e-05 -2.731e-05 0.00010795 2.7437e-05 0.00018252 -5.2551e-06 2.6551e-05 0.00018399 -3.875e-06 3.0088e-05 Shock to Response 3 ans = 10x2 table Orthogonal Generalized _________________________________________ _________________________________________ 0 0 0.0076083 0.013038 0.006466 0.009434 0.0073116 0.0021988 -0.0020086 0.0058379 0.0023108 -0.0010618 0.0031572 -0.00067127 0.00084299 0.0049047 0.00027687 0.0033197 -0.0030985 0.00091269 0.00069346 -4.6882e-06 0.0014793 0.00021826 0.001993 6.1109e-05 -0.00012102 0.00277 5.3838e-05 0.00046724 0.00050636 -0.00010115 0.00024511 -5.4815e-05 0.00027437 0.0004034 -0.00036814 0.00021062 3.6381e-06 0.00044188 0.00020705 5.8359e-05 0.00028783 -2.6426e-05 2.3079e-05 0.00036206 3.0686e-06 0.00011696 1.3105e-05 8.9361e-06 4.9558e-05 4.1567e-06 7.4706e-05 5.6331e-05 1.6913e-05 2.719e-05 -1.1202e-05 0.00011501 2.2025e-05 1.2756e-05 

If armairf shocks the first variable, then the impulse responses of all variables are equivalent between methods. The second and third pages illustrate that the generalized and orthogonal impulse responses are generally different. However, if InnovCov is diagonal, then both methods produce the same impulse responses.

Another difference between the two methods is that generalized impulse responses are invariant to the order of the variables. However, orthogonal impulse responses differ with varying variable order.