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[Fortran]Multiplying Matrices Using dgemm

[Fortran]Multiplying Matrices Using dgemm

[Fortran]Multiplying Matrices Using dgemm

I would like to multiply two arrays in Fortran using DGEMM (BLAS procedure).
I have written a simple program:


program matrix
  implicit none
  double precision mac(m,n),mac2(n,k),mac3(m,k)
  integer R,L
  integer m,n,k


  call FILLMATRIX(m,n,mac)
  call FILLMATRIX(n,k,mac2)
  call DGEMM("N","N",m,k,n,1.d0,mac,m,mac2,n,0.d0,mac3,m)

  WRITE(*,*)'Matrix C:'
    DO R=1,m
      write(*,*) (mac3(R,L),L=1,k)
    end do



    do  I=1,M
    do  J=1,N
      MATRIX(I,J) = I+2*J
    end do
    end do

  WRITE(*,*) 'Matrix:'
    do I=1,M
     write(*,*) (MATRIX(I,J),J=1,N)
    end do


And I get this result:


Matrix C:
    29.00000000000000        0.0000000000000000        0.0000000000000000     
    36.00000000000000        0.0000000000000000        0.0000000000000000     
    27.00000000000000        7.2315834086755357E-308   0.0000000000000000     
    34.00000000000000        1.0037966311151816E-317   0.0000000000000000     
Segmentation fault 
Could you point me where I have a mistake?
I will be very grateful for your help.

RE: [Fortran]Multiplying Matrices Using dgemm

It's surprising that your code compiled ran at all.

You've declared three arrays, mac, mac2 and mac3 with unknown sizes. m, n & k must have actual values before you declare mac, mac2 & mac3.

Put this statement before your Double Precision line and you'll be fine:
(note: this assumes fortran90 or higher. if you're only using an old fortran77 compiler, you need the older syntax to declare you integer parameters)

integer, parameter :: m=4, n=2, k=3


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