如何为矩阵分配内存？

Question

我想用Fortran 90为双元矩阵分配内存，下面是对应的C代码：

int dim = 1024;
double *M = (double *)malloc(dim*dim*sizeof(double));

我写了下面的代码，但我无法使用 i>=100 访问 M(i):

program matrix
INTEGER :: i,d
CHARACTER(len=32) :: arg
REAL*8 M(*)
POINTER(ptr_M, M)

d=0
if(iargc() == 1) then
    call getarg(1, arg)
    read(arg, '(I10)') d
end if
print '("Dimension=", i6)', d

!allocate and init matrix
ptr_M = malloc(d*d*8)
do i=1,d*d
    M(i) = i
end do

print '("M(i)=", f7.4)', M(100)
call free(ptr_M)

end program matrix

怎么了？

感谢大家，这是我的最终解决方案：

program matrix
IMPLICIT NONE
REAL, ALLOCATABLE :: M(:,:)
INTEGER :: i, j, d
CHARACTER(len=32) :: arg

!specify dimension with programm parameter
if(iargc() == 1) then
    call getarg(1, arg)
    read(arg, '(I10)') d
end if

!create and init matrix
ALLOCATE (M(d, d))
do i=1,d
    do j=1,d
        M(i, j) = (i - 1)*d+j
        write (*,*) "M(",i,",",j,")=",M(i, j)
    end do
end do
DEALLOCATE (M)

end program matrix

Answer 1

使用 ALLOCATABLE 数组，您可以分配一个具有 100 行和 200 列的矩阵，如下所示：

program xalloc
real, allocatable :: x(:,:)
allocate(x(100,200))
end program xalloc

如何为矩阵分配内存？

How to allocate memory for a matrix?

fortran

memory-management

matrix