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Numerical accuracy
Computers aren’t nearly so bright as your average junior high school student, so they use numerical methods which come up with approximate solutions. If you’d like a “more accurate” answer, you need to tell EViews to be more fussy. Click 
and choose the
Solver tab. Change Convergence to “1e-09”, to get that one extra digit of accuracy.
Vanity hint: In the problem at hand, all we’re doing is making the answer look pretty.
In more complicated problems a smaller convergence limit has the advantage that it helps assure that the computer reaches the right answer. The disadvantages are that the solution takes longer, and that sometimes if you ask for extreme accuracy no satisfactory answer can be found.
Accurately understanding accuracy: Don’t confuse numerical accuracy with model accuracy. The solver options control numerical accuracy. These options have nothing to do with the accuracy of your model or your data. The latter two are far more important. Unfortunately, you can’t improve model or data accuracy by clicking on a button.
Your Second Homework
Odds are that your second homework assignment in your first introductory macroeconomics class asked what would happen to GDP if G were to rise. In other words, how do the results of this new scenario differ from the baseline results?
Your Second Homework—375
Making Scenarios
EViews puts a single set of assumptions about the inputs to a model together with the resulting solution in a scenario. The solutions based on the original data are called the Baseline. So the solutions to our first homework problem are stored in the baseline scenario. Choosing Scenarios… from the View menu brings up the
Scenario Specification dialog with the Select Scenario tab showing. The Baseline scenario that’s showing was automatically created when we solved the model.
A look at the aliasing tab shows that the suffix for Baseline results is “_0.” The fields are greyed out because EViews assigns the suffix for the Baseline.
376—Chapter 15. Super Models
We want to ask what would happen in a world in which government spending were 10 (billion dollars) higher than it was in the real world. This is a new scenario, so click 
on the Select Scenario tab. Scenario 1 is associated with the alias “_1”. If you like, you can rename the new scenario to something more meaningful or change the suffix, but we’ll just click 
for now.
We want to instruct EViews to use different values of G in this scenario. We’ll create the series G_1 with the command:
series g_1 = g + 10
Hint: We chose the name “G_1” because the suffix has to match the scenario alias.
Overriding Baseline Data
Back in the model window click
and then right-click on G and choose Properties….
Your Second Homework—377
On the Properties dialog, check Use override in series in scenario to instruct EViews to substitute G_1 for G.
Now 
.
Hint: You can override an exogenous variable but you cannot override an endogenous variable because the latter would require a change to the structure of the model.
New series Y_1 and CONS_1 appear in the workfile. Return to Proc/Make Graph… in the model window, choose Listed Variables, list Y, and check Compare. As you can see in the dialog, many options are available. We’re asking for a comparison of the baseline solution to the new scenario. We can show the difference between the two— by checking one of the Deviations boxes—in either units or as a percentage.