对一串数字求和

Question

下面的这段代码显示：1 1.2 3 但是1 2.2 5.2这是预料之中的。哪里错了？

\documentclass[tikz]{standalone}

\begin{document}

\xdef\Sum{0}
\foreach \i in {1,1.2,3} {
    \pgfmathsetmacro\Sum{\Sum+\i}
    \Sum\ }

\end{document}

Answer 1

看起来宏的定义\Sum对于组来说是局部的。在下一次迭代中，它的内容会被遗忘，只有第一个全局定义会\xdef被保留。不过我对此不太了解。

这是一个可行的示例（但可能不是最好的方法）。

\documentclass[tikz]{standalone}

\begin{document}

\xdef\Sum{0}
\foreach \i in {1,1.2,3} {
    \xdef\Sum{\Sum+\i}
    \pgfmathparse{\Sum}\pgfmathresult\ }

\end{document}

输出符合预期：1.0 2.2 5.2

Answer 2

和expl3：

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand\sumlist{ m }
 {
  \tarass_sum_list:n { #1 }
 }

\fp_new:N \l__tarass_partial_sum_fp

\cs_new_protected:Npn \tarass_sum_list:n #1
 {
  \fp_zero:N \l__tarass_partial_sum_fp
  \clist_map_inline:nn { #1 }
   {
    \fp_add:Nn \l__tarass_partial_sum_fp { ##1 }
    $\fp_use:N \l__tarass_partial_sum_fp$
    \ %
   }
   \unskip % remove the last space
 }
\ExplSyntaxOff

\begin{document}

\sumlist{1,1.2,3}

\sumlist{1,-1.2,3}

\end{document}

Answer 3

这是一个可以准确打印所需数字总数的版本。

嗯...这不是所问的。抱歉。

好的，所以我更新了代码以打印所要求的部分和。正如已经指出的那样，问题\foreach是限制范围的本地组之一。循环\xintFor 没有xinttools这个问题。因此我在这里使用它。我在这里使用xintfrac包的算法。但\xintFor 循环可以用作pgfmath数学引擎。

然后，我之前关注的第二个元素是打印一个十进制数，其位数恰好是所需的位数。请注意，此处的宏与任意长的数字兼容。

代码：

\documentclass{article}

\usepackage{xintfrac}
\usepackage{xinttools}

% Let's first do the partial sums as fixed point numbers.
% We hardcode \Sum macro to hold the partial sums
\newcommand\TarassSumList [1]{\def\Sum{0}\xintFor ##1 in {#1}\do
       {\oodef\Sum{\xintAdd{\Sum}{##1}}%
        \xintRound{4}{\Sum}%
        \xintifForLast{}{, }}}

% let's now do it again but printing with the number of necessary
% digits:

% 
% We abstract some command from code below (an expandable version
% should be added to xint package)

\makeatletter
\def\ReduceDec@helper #1[#2]{#2}% duplicate of \sumlist@helper
\newcommand\ReduceDec [1]{%
         \oodef\ReduceDec@X {\xintREZ{#1}}%
         \oodef\ReduceDec@N {\expandafter\ReduceDec@helper\ReduceDec@X }%
         \ifnum\ReduceDec@N<\z@
            \oodef\ReduceDecResult{\xintTrunc {-\ReduceDec@N}{\ReduceDec@X}}%
         \else
            \oodef\ReduceDecResult{\xintNum \ReduceDec@X}%
         \fi }
\makeatother

\newcommand\TarassSumListB [1]{\def\Sum{0}\xintFor ##1 in {#1}\do
       {\oodef\Sum{\xintAdd{\Sum}{##1}}%
        \ReduceDec{\Sum}\let\Sum\ReduceDecResult
         \Sum
        \xintifForLast{}{, }}}

% earlier answer which concentrated on the printing of decimal number with
% exactly the needed number of digits.

% sum decimal numbers, and print the result with exactly as
% many digits as necessary after the decimal mark

% It would be  quite easier to print a truncation or rounding to a
% given number of digits after decimal mark (\xintTrunc or \xintRound
% and the whole thing would be completely expandable)

% To avoid scaring people, I did not make this more challenging version
% expandable...

% And it is to be used only for decimal numbers or scientific number on
% input, no fractions like 3/7.

\makeatletter
\def\sumlist@helper #1[#2]{#2}% there should be a macro in xintfrac for that
\newcommand\sumlist [1]{%
         \oodef\sumlist@S {\xintREZ{\xintSum{\xintCSVtoList {#1}}}}%
         \oodef\sumlist@N {\expandafter\sumlist@helper\sumlist@S }%
         \ifnum\sumlist@N<\z@
            \xintTrunc {-\sumlist@N}{\sumlist@S}%
         \else
            \xintNum \sumlist@S
         \fi}
\makeatother

\begin{document}\thispagestyle{empty}

Fixed point numbers (4 decimal digits):

\TarassSumList{1,1.2,3}

\TarassSumList{1,-1.2,3}

\TarassSumList {1.23, 3.31, -0.54}

\TarassSumList {1.234, 5.6789, 3.211768, -17.28929}

\TarassSumList {1.234, 5.6789, 3.211768, -17.28929, 13.004622}

\TarassSumList {1.23e-3, 3.25e-3, 17.123e-4}

Numbers with as many digits as necessary:

\TarassSumListB{1,1.2,3}

\TarassSumListB{1,-1.2,3}

\TarassSumListB {1.23, 3.31, -0.54}

\TarassSumListB {1.234, 5.6789, 3.211768, -17.28929}

\TarassSumListB {1.234, 5.6789, 3.211768, -17.28929, 13.004622}

\TarassSumListB {1.23e-3, 3.25e-3, 17.123e-4}


% \sumlist{1,1.2,3}

% \sumlist{1,-1.2,3}

% \sumlist {1.23, 3.31, -0.54}

% \sumlist {1.234, 5.6789, 3.211768, -17.28929}

% \sumlist {1.234, 5.6789, 3.211768, -17.28929, 13.004622}

% \sumlist {1.23e-3, 3.25e-3, 17.123e-4}

% \sumlist {100, 200}

\end{document}

Answer 4

只需练习渐近线使用内置sum(a)函数计算给定实数数组所有元素的总和a。

real[] a={1,1.2,-5};
write(a);

real T=sum(a);
write("The sum of all elements is");
write(T);