从函数中返回一个数组并将其存储在主程序中 [英] Return an array from a function and store it in the main program

问题描述

这是主程序:

      PROGRAM integration
      EXTERNAL funct
      DOUBLE PRECISION funct, a , b, sum, h
      INTEGER n, i
      REAL s

      PARAMETER (a = 0, b = 10, n = 200)  

      h = (b-a)/n
      sum = 0.0

      DO i = 1, n
         sum = sum+funct(i*h+a)
      END DO

      sum = h*(sum-0.5*(funct(a)+funct(b)))

      PRINT *,sum

      CONTAINS

      END     

下面是函数funct(x)

And below is the Function funct(x)

      DOUBLE PRECISION FUNCTION funct(x)
      IMPLICIT NONE

      DOUBLE PRECISION x
      INTEGER K

      Do k = 1,10
      funct = x ** 2 * k
      End Do

      PRINT *, 'Value of funct is', funct

      RETURN
  END

我希望主程序中的 'Sum' 打印函数 funct(x) 中 10 个不同 k 值的 10 个不同总和.

I would like the 'Sum' in the Main Program to print 10 different sums over 10 different values of k in Function funct(x).

我已经尝试过上面的程序，但它只是编译了 Funct() 的最后一个值，而不是总共 10 个不同的值.

I have tried the above program but it just compiles the last value of Funct() instead of 10 different values in sum.

推荐答案

数组结果需要显式接口.您还需要使用 dimension 语句将 funct 和 sum 调整为实际上是数组.使用显式接口需要 Fortran 90+(感谢@francescalus 和@VladimirF 的提示)并且非常乏味:

Array results require an explicit interface. You would also need to adjust funct and sum to actually be arrays using the dimension statement. Using an explicit interface requires Fortran 90+ (thanks for the hints by @francescalus and @VladimirF) and is quite tedious:

        PROGRAM integration
        INTERFACE funct
          FUNCTION funct(x) result(r)
            IMPLICIT NONE
            DOUBLE PRECISION r
            DIMENSION r( 10 )
            DOUBLE PRECISION x
          END FUNCTION
        END INTERFACE
        DOUBLE PRECISION a , b, sum, h
        DIMENSION sum( 10)
        INTEGER n, i

        PARAMETER (a = 0, b = 10, n = 200)  

        h = (b-a)/n
        sum = 0.0

        DO i = 1, n
           sum = sum+funct(i*h+a)
        END DO

        sum = h*(sum-0.5*(funct(a)+funct(b)))

        PRINT *,sum

        END  

        FUNCTION funct(x)
        IMPLICIT NONE
        DOUBLE PRECISION funct
        DIMENSION funct( 10)
        DOUBLE PRECISION x
        INTEGER K

        Do k = 1,10
          funct(k) = x ** 2 * k
        End Do

        PRINT *, 'Value of funct is', funct

        RETURN
        END

如果可以，您应该切换到更现代的标准，例如 Fortran 90+，并使用 modules.它们自动提供接口，这使得代码更简单.

If you can, you should switch to a more modern Standard such as Fortran 90+, and use modules. These provide interfaces automatically, which makes the code much simpler.

或者，您可以将 k 上的循环从函数中取出，并按元素执行求和.这将是有效的 FORTRAN 77:

Alternatively, you could take the loop over k out of the function, and perform the sum element-wise. This would be valid FORTRAN 77:

        PROGRAM integration
c       ...
        DIMENSION sum( 10)
c       ...
        INTEGER K
c       ...
        DO i = 1, n
          Do k = 1,10
            sum(k)= sum(k)+funct(i*h+a, k)
          End Do
        END DO
c       ...

请注意，我将 k 传递给函数.需要相应调整:

Notice that I pass k to the function. It needs to be adjusted accordingly:

        DOUBLE PRECISION FUNCTION funct(x,k)
        IMPLICIT NONE
        DOUBLE PRECISION x
        INTEGER K

        funct = x ** 2 * k

        PRINT *, 'Value of funct is', funct

        RETURN
        END

这个版本只返回一个标量并填充主程序中的数组.

This version just returns a scalar and fills the array in the main program.

除此之外，我不确定使用名为 sum 的变量是否明智.有一个同名的内在函数.这可能会导致一些混乱...

Apart from that I'm not sure it is wise to use a variable called sum. There is an intrinsic function with the same name. This could lead to some confusion...

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