## 数学代写|matlab代写|Passing Structures to Functions

An entire structure can be passed to a function or individual fields can be passed. For example, here are two different versions of a function that calculates the profit on a software package. The profit is defined as the price minus the cost.

In the first version, the entire structure variable is passed to the function, so the function must use the dot operator to refer to the price and cost fields of the input argument.In the second version, just the price and cost fields are passed to the function using the dot operator in the function call. These are passed to two scalar input arguments in the function header, so there is no reference to a structure variable in the function itself, and the dot operator is not needed in the function.It is important, as always with functions, to make sure that the arguments in the function call correspond one-to-one with the input arguments in the function header.

In the case of calcprof, a structure variable is passed to an input argument, which is a structure. For the second function calcprof2, two individual numbers (which could be fields from a structure) which are double values, are passed to two double input arguments.

## 数学代写|matlab代写|Vectors of Structures

In many applications, including database applications, information would normally be stored in a vector of structures, rather than in individual structure variables. For example, if the computer super mart is storing information on all of the software packages that it sells, it would likely be in a vector of structures such as the following:

In this example, packages is a vector that has three elements. It is depicted as a column vector, although it may be a row vector. Each element is a structure consisting of four fields: item_no, cost, price, and code. It may look like a matrix, which has rows and columns, but it is, instead, a vector of structures.

This vector of structures can be created several ways. One method is to create a structure variable, as shown earlier, to store information on one software package. This can then be expanded to be a vector of structures by assigning to packages (2) and packages(3).

Alternatively, the first structure could be treated as a vector to begin with by assigning to packages(1), then packages(2), then packages(3).

Both of these methods, however, involve extending the vector. As we have already seen, preallocating any vector in MATLAB is more efficient than extending it. There are several methods of preallocating the vector. By starting with the last element, MATLAB would create a vector with that many elements. Then, the elements from 1 through end-1 could be initialized. For example, for a vector of structures that has three elements, start with the third element.

# matlab代考

## 数学代写|matlab代写|Vectors of Structures

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