Databases
StackOverflow2013
Postsdbo
POFortran Matrix Multiplication isn't giving the right answers
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POFortran Matrix Multiplication isn't giving the right answers
    primarykey
    data
    text
    <p>I've got a matrix calculator program, but I'm getting the wrong answer for my dot product multiplier. </p> <p>Here's my multiply subroutine:</p> <pre><code>subroutine multiply(m1,m2,res,row1,row2,col1,col2) integer, intent(in) :: row1,row2,col1,col2 real, intent(in), dimension(row1,col1) :: m1 real, intent(in), dimension(row2,col2) :: m2 real, intent(out), dimension(row1,col2) :: res integer :: i,j,k do i = 1, col2 do j = 1, col1 res(j, i) = 0 enddo do j = 1, col1 do k = 1, row1 res(k, i) = res(k, i) + m1(k, j)*m2(j, i) enddo enddo enddo </code></pre> <p>And here's my output, just in case that's the problem.</p> <pre><code> subroutine output(r,c,matrix,name) integer, intent(in) :: r integer, intent(in):: c character(len=10) :: name real, intent(out), dimension(3,3) :: matrix integer i,j print *,name do i = 1, r write(*,"(100F6.1)") ( matrix(i,j), j=1,c ) enddo end subroutine </code></pre> <p>If it helps, it works excellently for a 3x3 matrix, but not for two rectangular matrix. Here's what happens when I do a 2x3 * 3x2 matrix. At this point, i'm desperate for help. Anything you could suggest would be great. Thanks!</p> <p><img src="https://i.stack.imgur.com/APC2W.png" alt="enter image description here"></p> <p>EDIT: Here's all of my code in its current state with your suggestions.</p> <pre><code> PROGRAM G6P5 integer :: r1,r2,c1,c2,i,j,k,s real :: input real, dimension (3,3) :: mat1, mat2, rmat write (*,*) 'Please make a selection:' write (*,*) 'Enter 1 to add matrices' write (*,*) 'Enter 2 to subtract matrices' write (*,*) 'Enter 3 to multiply matrices' write (*,*) 'Enter 4 to transpose a matrix' write (*,*) 'Enter 5 to quit' read *, s select case (s) case (1) print *, 'Enter # of rows &amp; columns (1-10) (ex. 3 3 = 3x3)' read *, r1,c1 print *, 'Matrix 1:' call fillmatrix(r1,c1,mat1) r2 = r1 c2 = c1 print *, 'Matrix 2:' call fillmatrix(r2,c2,mat2) call output(r1,c1,mat1,'Matrix 1: ') call output(r2,c2,mat2,'Matrix 2: ') rmat = mat1+mat2 call output(r1,c1,rmat,'Sum: ') case (2) print *, 'Enter # of rows &amp; columns (1-10) (ex. 3 3 = 3x3)' read *, r1,c1 print *, 'Matrix 1:' call fillmatrix(r1,c1,mat1) r2 = r1 c2 = c1 print *, 'Matrix 2:' call fillmatrix(r2,c2,mat2) rmat = mat1-mat2 call output(r1,c1,mat1,'Matrix 1: ') call output(r2,c2,mat2,'Matrix 2: ') call output(r1,c1,rmat,'Sum: ') case (3) print *, 'Enter # of rows &amp; columns for matrix 1' print *, '(1 through 10, ex: 3 3 = 3x3)' read *, r1,c1 print *, 'Matrix 1:' call fillmatrix(r1,c1,mat1) print *, 'Enter # of rows &amp; columns for matrix 2' print *, '(1 through 10, ex: 3 3 = 3x3)' read *, r2,c2 print *, 'Matrix 2:' call fillmatrix(r2,c2,mat2) if (c1.eq.r2) then call multiply(mat1,mat2,rmat,r1,r2,c1,c2) call output(r1,c1,mat1,'Matrix 1: ') call output(r2,c2,mat2,'Matrix 2: ') call output(r1,c2,rmat,'Product: ') end if case (4) print *, 'Enter # of rows &amp; columns for matrix 1' print *, '(1 through 10, ex: 3 3 = 3x3)' read *, r1,c1 print *, 'Matrix 1:' call fillmatrix(r1,c1,mat1) call transpose(mat1,rmat,r1,c1) call output(r1,c1,rmat,'Transpose:') case (5) print *,'5' case default print *,'default' end select ! call fillmatrix(rows,columns,mat1) ! write (*,*) matrix1 END PROGRAM subroutine fillmatrix(r,c,matrix) integer, intent(in) :: r integer, intent(in):: c real, intent(out), dimension(3,3) :: matrix integer i,j do i=1,r do j = 1,c write (*,'(A,I2,A,I2,A)') 'Enter value (',i,',',j,').' read*, matrix(i,j) enddo enddo end subroutine subroutine multiply(m1,m2,res,row1,row2,col1,col2) integer, intent(in) :: row1,row2,col1,col2 real, intent(in), dimension(row1,col1) :: m1 real, intent(in), dimension(row2,col2) :: m2 real, intent(out), dimension(row1,col2) :: res integer :: i,j,k res = 0 do i = 1, row1 do j = 1, col2 do k = 1, col1 ! col1 must equal row2 res(i, j) = res(i, j) + m1(i, k)*m2(k, j) enddo ! k enddo ! j enddo ! i end subroutine subroutine transpose(m1,res,row,col) integer, intent(in) :: row,col real, intent(in), dimension(row,col) :: m1 real, intent(out), dimension(row,col) :: res integer :: i,j,k do i = 1,col do j = 1,row res(i,j) = m1(j,i) enddo enddo end subroutine subroutine output(r,c,matrix,name) integer, intent(in) :: r integer, intent(in):: c character(len=10) :: name real, intent(in), dimension(r,c) :: matrix integer i,j print *,name do i = 1, r write(*,"(100F6.1)") ( matrix(i,j), j=1,c ) enddo end subroutine </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USAlex Kibler
    1. USAlex Kibler
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POFortran Matrix Multiplication isn't giving the right answers
      1. This table or related slice is empty.
      1. VTUpMod
    1. COCan you just copy and paste your output? It makes it difficult to copy and paste those numbers into my editor to help you. Also, what matrix output do you expect?
      singulars
      1. POFortran Matrix Multiplication isn't giving the right answers
      1. USSethMMorton
    2. COOh, sure, sorry. Well now my output is this ` Matrix 1: ` ` 1.0 0.0 5.0` ` 4.0 2.0 0.0` ` Matrix 2: ` ` 6.0 4.0` ` 3.0 2.0` ` 3.0 5.0` ` Product: ` ` 21.0 29.0` ` 30.0 20.0` However, I entered 1 2 3 4 5 6 for the first matrix
      singulars
      1. POFortran Matrix Multiplication isn't giving the right answers
      1. USAlex Kibler
    3. COEach time you pass your matrix to a subroutine, do this instead: `call sub(r1,c1,mat(1:r1,1:c1))`. If that works, I'll explain why in my answer.
      singulars
      1. POFortran Matrix Multiplication isn't giving the right answers
      1. USSethMMorton
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload