### 计算机代写|并行计算作业代写Parallel Computing代考|Temporary Variables

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• Statistical Computing 统计计算
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• Foundations of Data Science 数据科学基础

## 计算机代写|并行计算作业代写Parallel Computing代考|Temporary Variables

A temporary variable is any variable that is the target of a direct, nonindexed assignment, but is not a reduction variable. In the following parfor-loop, a and $d$ are temporary variables:
$\mathrm{a}=\theta$;
$z=\theta$;
$r=\operatorname{rand}(1,10)$;
parfor $i=1: 10$
a $=i ; \quad$ \& Variable a is temporary
$z=z+i ;$
$z=z+i$ if $i<=5$ end end
end
In contrast to the behavior of a for-loop, MATLAB clears any temporary variables before each
iteration of a parfor-loop. To help ensure the independence of iterations, the values of temporary
variables cannot be passed from one iteration of the loop to another. Therefore, temporary variables
must be set inside the body of a parfor-loop, so that their values are defined separately for each
iteration.
MATLAB does not send temporary variables back to the client. A temporary variable in a parfor-loop has no effect on a variable with the same name that exists outside the loop. This behavior is different from ordinary for-loops.

## 计算机代写|并行计算作业代写Parallel Computing代考|Uninitialized Temporaries

Temporary variables in a parfor-loop are cleared at the beginning of every iteration. MATLAB can sometimes detect cases in which loop iterations use a temporary variable before it is set in that iteration. In this case, MATLAB issues a static error rather than a run-time error. There is little point in allowing execution to proceed if a run-time error is guaranteed to occur. This kind of error often arises because of confusion between for and parfor, especially regarding the rules of classification of variables. For example:
b = true;
parfor $i=1: n$
if b Eas some_condition(i)
do_something(i);
$b=$ false;
end
$b=$ true;
parfor $i=1: n$
if b Eas some_condition(i)
do_something(i);
$\quad b=$ false;
end
end
This loop is acceptable as an ordinary for-loop. However, as a parfor-loop, b is a temporary variable because it occurs directly as the target of an assignment inside the loop. Therefore it is cleared at the start of each iteration, so its use in the condition of the if is guaranteed to be uninitialized. If you change parfor to for, the value of $b$ assumes sequential execution of the loop. In that case, do_something $(i)$ is executed only for the lower values of $i$ until b is set false.

## 计算机代写|并行计算作业代写Parallel Computing代考|Temporary Variables Intended as Reduction Variables

Another common cause of uninitialized temporaries can arise when you have a variable that you intended to be a reduction variable. However, if you use it elsewhere in the loop, then it is classified as a temporary variable. For example:
$s=\theta$;
parfor $i=1: n$
$s=s+f(i)$;
if (s> whatever)
end
end
Another common cause of uninitialized temporaries can arise when you have a variable that you
intended to be a reduction variable. However, if you use it elsewhere in the loop, then it is classified
as a temporary variable. For example:
$s=0$;
parfor $i=1: n$
$\quad s=s+f(i)$;
$\quad$ if $(s>$ whatever)
end
end
If the only occurrences of s are the two in the first statement of the body, s would be classified as a
reduction variable. But in this example, $s$ is not a reduction variable because it has a use outside of
reduction assignments in the line s $>$ whatever. Because s is the target of an assignment (in the
first statement), it is a temporary. Therefore MATLAB issues an error, but points out the possible
connection with reduction.
If you change parfor to for, the use of s outside the reduction assignment relies on the iterations
being performed in a particular order. In a parfor-loop, it matters that the loop “does not care”
about the value of a reduction variable as it goes along. It is only after the loop that the reduction
value becomes usable.
If the only occurrences of s are the two in the first statement of the body, s would be classified as a
reduction variable. But in this example, $s$ is not a reduction variable because it has a use outside of
reduction assignments in the line $s>$ whatever. Because $s$ is the target of an assignment (in the
first statement), it is a temporary. Therefore MATLAB issues an error, but points out the possible
connection with reduction.
If you change parfor to for, the use of s outside the reduction assignment relies on the iterations being performed in a particular order. In a parfor-loop, it matters that the loop “does not care” about the value of a reduction variable as it goes along. It is only after the loop that the reduction value becomes usable.

## 计算机代写|并行计算作业代写Parallel Computing代考|Temporary Variables

r=兰特⁡(1,10);

end

parfor 循环的每次迭代之前清除所有临时变量。为了帮助确保迭代的独立性，临时

MATLAB 不会将临时变量发送回客户端。parfor 循环中的临时变量对循环外存在的同名变量没有影响。这种行为不同于普通的 for 循环。

## 计算机代写|并行计算作业代写Parallel Computing代考|Uninitialized Temporaries

parfor 循环中的临时变量在每次迭代开始时都会被清除。MATLAB 有时可以检测到循环迭代在该迭代中设置之前使用临时变量的情况。在这种情况下，MATLAB 会发出静态错误而不是运行时错误。如果保证会发生运行时错误，则允许继续执行几乎没有意义。这种错误通常是由于混淆了 for 和 parfor 造成的，尤其是在变量分类规则方面。例如：
b = true；

if b Eas some_condition(i)
do_something(i);
b=错误的;

b=真的;

if b Eas some_condition(i)
do_something(i);
b=错误的;
end
end

s=θ;

s=s+F(一世);
if (s> whatever)
end
end

s=0;

s=s+F(一世);

end
end

## 有限元方法代写

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。