Question

我正在Fortran 90中做一些数值练习。当我试图用交替的登录参数做一个总和时，我注意到（以我做的方式）Fortran不知道怎么做去做。

例如，我想在k（1（1）^ k）/ 2k的1到10之间做一个总和，所以我做的是

sumk = 0
do k = 1,10
   sumk = ((-1)**k)/(2*k) + sumk
end do

但是输出是sumk = 1.我做错了什么？

Answer 1

如果k是整数，则表示您正在执行整数运算。这些可能无法达到预期效果，例如： 1/2 = 0。当然，使用浮点数会产生0.5，但转换为整数会产生0。

因此，基本上，您添加到sumk的部分在您的情况下始终为零，最终会导致sumk=0。为防止这种情况，您需要使用浮点数：

  sumk = real(((-1)**k))/real(2*k) + sumk

然后，结果是-0.322817445（我使用Wolfram Alpha验证）。

当然，有几种方法可以改进这一点，例如迭代计算(-1)**k，或者通过模运算替换它。

Answer 2

我在Fortran中的最佳经验总是声明您希望它们在您的代码中使用的数字，就像您使用变量一样。当您想要使用Double use 1.0e0时，如果您想使用Single use 1，并且想要使用Integer时使用sumk = 0.0d0 do k = 1,10 sumk = ((-1.0d0)**dble(k))/(2.0d0*dble(k)) + sumk end do。所以在你的情况下，我建议像：

Configuration file: /Users/MyName/Projects/blog/_config.yml
/Users/MyName/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- typogruby (LoadError)
from /Users/MyName/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/MyName/Projects/blog/_plugins/enhanced_kramdown.rb:3:in `<top (required)>'
from /Users/MyName/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/MyName/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:74:in `block (2 levels) in require_plugin_files'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:73:in `each'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:73:in `block in require_plugin_files'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:72:in `each'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:72:in `require_plugin_files'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:18:in `conscientious_require'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/site.rb:79:in `setup'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/site.rb:41:in `initialize'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `new'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `process'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/lib/jekyll/commands/serve.rb:26:in `block (2 levels) in init_with_program'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `call'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `block in execute'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `each'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `execute'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary/program.rb:42:in `go'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/mercenary-0.3.5/lib/mercenary.rb:19:in `program'
from /Users/MyName/.rvm/gems/ruby-2.1.1/gems/jekyll-2.5.3/bin/jekyll:20:in `<top (required)>'
from /Users/MyName/.rvm/gems/ruby-2.1.1/bin/jekyll:23:in `load'
from /Users/MyName/.rvm/gems/ruby-2.1.1/bin/jekyll:23:in `<main>'
from /Users/MyName/.rvm/gems/ruby-2.1.1/bin/ruby_executable_hooks:15:in `eval'
from /Users/MyName/.rvm/gems/ruby-2.1.1/bin/ruby_executable_hooks:15:in `<main>'

顺便说一句，如果你没有任何内存问题，我总是会使用双精度。

与交替登录参数相加

2 个答案: