通过正确定义索引列表来提高代码效率 [英] Improving efficiency of code by correctly defining a list of indices

问题描述

我问了这个问题避免通过重复复制代码-结构化if语句/do循环，以确定如何使我的代码更高效.该解决方案极大地帮助了我，如下所示.

I asked this question avoid duplicating code by re-structuring if statement/do loop in order to determine how I could make my code more efficient. The solution greatly helped me and is shown below.

function grad(psi)
  implicit none
  integer, parameter :: nx = 24, ny = 24, nxx = nx / 2, nyy = ny / 2
  real, parameter :: pi = 4 * atan(1.0), f0 = pi ** 2 * 1.3
  complex, dimension(3,3,-nx:nx,-ny:ny) :: psi, grad

  grad(:,:,-nx+1:nx-1,-ny+1:ny-1) = psi(:,:,-nx+2:nx,-ny+1:ny-1)
  grad(:,:,0,0) = psi(:,:,1,0)
  grad(:,:,[-nxx,nxx],[-nyy,nyy,ny]) = psi(:,:,[-nxx+1,nxx+1],[-nyy,nyy,ny]) - f0 * psi(:,:,[-nxx,nxx],[-nyy,nyy,ny])

end

但是我现在需要进一步优化代码.

However I need to optimize my code even more now.

在上面的示例中，有一个部分由

In the example above there is a portion given by

grad(:,:,[-nxx,nxx],[-nyy,nyy,ny]) = psi(:,:,[-nxx+1,nxx+1],[-nyy,nyy,ny]) - ...

通过考虑列表-nxx,-nyy, -nxx, nyy,等的所有组合有效地完成了我所需要的工作.

which effectively does what I need by taking into account all the combinations of the lists -nxx,-nyy, -nxx, nyy, etc.

但是，我需要的索引列表比[-nxx,nxx],[-nyy,nyy]大得多.我真的需要类似[-nxx,nxx,-nxx1,nxx1,-nxx2,nxx2,-nxx3,nxx3], [-nyy,nyy,-nyy1,nyy1,-nyy2,nyy2,-nyy3,nyy3]等的东西，其中nxx = nx/2, nxx1 = nx/4, nxx2 = nx/8, nxx3 = nx/16等.

However the list of indices I need is much bigger than just [-nxx,nxx],[-nyy,nyy]. I really need something like [-nxx,nxx,-nxx1,nxx1,-nxx2,nxx2,-nxx3,nxx3], [-nyy,nyy,-nyy1,nyy1,-nyy2,nyy2,-nyy3,nyy3] etc where nxx = nx/2, nxx1 = nx/4, nxx2 = nx/8, nxx3 = nx/16 etc.

有没有一种方法可以有效地做到这一点?例如，我可以只定义一个变量，例如:

Is there a way I can do this efficiently? For example, can I just define a single variable such as :

integer : Listx, Listy

   Listx = [-nxx,nxx,-nxx1,nxx1,-nxx2,nxx2,-nxx3,nxx3]
   Listy = [-nyy,nyy,-nyy1,nyy1,-nyy2,nyy2,-nyy3,nyy3]

然后有类似的东西

grad(:,:,Listx,Listy) = psi(:,:,Listx+1,Listy) - ...

我确实尝试过这样做，但是将Listx，Listy定义为整数似乎会带来问题.我尝试如下:

I did try doing this, but defining Listx, Listy as integers seems to be giving problems. I tried as follows:

Integer :: Listx, Listy

   Listx = [-nxx,nxx,-nxx1,nxx1,-nxx2,nxx2,-nxx3,nxx3]
   Listy = [-nyy,nyy,-nyy1,nyy1,-nyy2,nyy2,-nyy3,nyy3]

但是在编译时，Fortran告诉我不兼容的等级0，并且分配给..."

but then upon compiling Fortran tells me that "Incompatible ranks 0 and in assignment at ..."

如何正确定义?谢谢

推荐答案

如注释中所述，您在数组的声明中缺少dimension属性:

As said in the comments, you are missing the dimension attribute in the declaration of the arrays:

Integer :: Listx(8), Listy(8)

这应该可以解决您的问题.任何结果为rank-1数组的表达式都可以用作向量下标索引器.

This should solve your problem. Any expression that results to a rank-1 array is allowed as a vector subscript indexer.

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