![]() Hence the logical value of the expression is FALSE for \(a=2\) and TRUE for all other values of a. The numerical expression is zero if a equals 2, and non-zero otherwise. Here the numerical expression \((2*a - 4)\) is the logical condition. The following example illustrates this point. Numerical expressions may serve as logical conditions: a result of zero is treated as the logical value FALSE and a non-zero result is treated as the logical value TRUE. Logical Conditions: Numerical Expressions In all these examples a and b are scalars, s, t, u and v are parameters, and i and j are sets. ![]() In this section we use many examples to illustrate the concepts that are being introduced. In the following subsections this is shown in the context of simple conditional assignments with the dollar operator on the left-hand side (compare section Dollar on the Left). Logical conditions may be numerical expressions and numerical relations, they may refer to set membership and they may also contain acronyms. Logical conditions are special expressions that evaluate to a value of either TRUE or FALSE. However, variable attributes are allowed. Note Logical conditions used with the dollar operator cannot contain variables. These topics are covered in later sections of this chapter. Conditional expressions may be used in the context of assignments, indexed operations and equations. Logical conditions may take various forms, they are introduced in the next section. To make it clear, this conditional assignment may be read as: ' given that b is greater than 1.5, a equals 2'. If the condition is not satisfied, no assignment is made. Note that the term is the scalar a and the logical condition is the expression \((b > 1.5)\). This can be written in GAMS using the dollar operator as follows. The dollar operator may be read as under the condition that the following logical_condition evaluates to TRUE (or is unequal 0).Ĭonsider the following simple condition, where a and b are scalars. Here, term can be a number, a (indexed) symbol, and also a complex expression. The general syntax for a conditional expression is: term $ logical_condition The dollar operator is one of the most powerful features in GAMS. These can be found in the chapter Programming Flow Control Features. Programming flow control features such as the if statement, the loop, the while statement, and the for statement are not covered in this chapter. We will conclude the chapter by showing that in certain cases conditions may be modeled using filtering sets instead of the dollar operator. Next, we will discuss how dollar conditions are used to build conditional assignments, conditional indexed operations and conditional equations. This chapter is organized as follows: We will introduce the general form of the dollar condition first and then we will focus on the various types of logical conditions. Exceptions such as these may easily be modeled with a logical condition combined with the dollar operator '$', a very powerful feature of GAMS introduced in this chapter. For example, heavy trucks may not be able to use a particular route because of a weak bridge, or some sectors in an economy may not produce exportable products. The index operations already described are very powerful, but it is necessary to allow for exceptions of one sort or another. Anyway, there seems to be something wrong with the shortcuts while using a non-US layout.This chapter deals with the way in which conditional assignments, expressions and equations are made in GAMS. Shortcuts for other things than the assignment sign work fine but that's probably because most of the keys match up across different layouts e.g. The same thing does not work on desktop rstudio. The assignment operator shortcut is displayed as Alt - there as well but it only works if I press Alt , I think because an US - is where I have on my layout. I can assign Alt - to <- and it will display as Alt - but won't work in the editor.Ī similar issue happens in rstudio cloud, where, again, I can use my local keyboard layout just fine in the editor but shortcuts seem to want a different keyboard layout. For example if I assign Alt on my keyboard, I will display Alt = in the little text box, but Alt will work in the editor. Looking around in the Modify Keyboard Shortcuts window, I think the shortcuts engine assumes an English(US?) keyboard, which is not what I'm using. ![]() Pressing Alt - I would expect <- to be created in the editor, however after updating to 1.2.468, I only get a. ![]()
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