# Printing a matrix of unknown size to file preserving the shape **URL:** \ **Category:** Uncategorized\ **Created:** [October 2, 2021, 12:05pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985 "2021-10-02T12:05:41Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Ashok](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ashok](https://fortran-lang.discourse.group/u/Ashok)\ **Post date:** [October 2, 2021, 12:05pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/1 "2021-10-02T12:05:41Z")
Hi ! Can somebody please tell me how to print a matrix of unknown size to file as it is. How to set the format statement? Is there a way to parameterize format statement using Lbound and Ubound ? For example 2 x 3 matrix 2 3 4 3 4 5 should be printed as it is to the console or file. Thanks. ---
**Author:** ![mecej4](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/mecej4/32/855_2.png) [@mecej4](https://fortran-lang.discourse.group/u/mecej4)\ **Post date:** [October 2, 2021, 12:25pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/2 "2021-10-02T12:25:37Z")
> [@Ashok](#): > > … should be printed as it is to the console or file. What do you mean by “as it is”? On pencil and paper? Bits in IEEE floating point format in the computer? A hexadecimal string representation thereof? If you mean formatted output on a computer display, in decimal notation, for matrices of modest size, this can be done. Many numerical libraries such as NAG and IMSL provide subroutines for this purpose. ---
**Author:** ![Ashok](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ashok](https://fortran-lang.discourse.group/u/Ashok)\ **Post date:** [October 2, 2021, 12:30pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/3 "2021-10-02T12:30:25Z")
Sorry of the ambiguity. By “as it is” I mean in decimal notation. Like if the matrix in the memory is 2 x 3, if we print normally it will come out in a column straight line. for example: 2 3 4 3 4 5 will come as 2 3 3 4 4 5 But if I don’t know the size (i.e 2 x 3), but when I print it - I should be able to see: 2 3 4 3 4 5 in the file. ---
**Author:** ![Beliavsky](https://avatars.discourse-cdn.com/v4/letter/b/ba8739/32.png) [@Beliavsky](https://fortran-lang.discourse.group/u/Beliavsky)\ **Post date:** [October 2, 2021, 12:48pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/4 "2021-10-02T12:48:19Z")
I think this program does what you want, in two ways, although the second does assume you know how many columns the matrix has. ```auto program main implicit none integer, parameter :: n1 = 2, n2 = 3 integer :: i,mat(n1,n2) mat(1,:) = [2,3,4] mat(2,:) = [3,4,5] do i=1,n1 write (*,"(*(1x,i6))") mat(i,:) ! unlimited format used, with 6 positions for each integer, separated by a space end do write (*,"(3(1x,i6))") transpose(mat) ! Alternative using format reversion. Transpose used because Fortran arrays are column major. end program main ``` Output: ```auto 2 3 4 3 4 5 2 3 4 3 4 5 ``` ---
**Author:** ![mecej4](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/mecej4/32/855_2.png) [@mecej4](https://fortran-lang.discourse.group/u/mecej4)\ **Post date:** [October 2, 2021, 1:05pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/5 "2021-10-02T13:05:41Z")
> [@Ashok](#): > > But if I don’t know the size (i.e 2 x 3), but when I print it - I should be able to see: If you don’t know the size, what you print would likely be a false representation. If you have six elements (and you know that you have six), the matrix could be (6 X 1), (3 X 2), (2 X 3) or (1 X 6). You could have used some storage scheme other than “dense storage”. ---
**Author:** ![Ashok](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ashok](https://fortran-lang.discourse.group/u/Ashok)\ **Post date:** [October 2, 2021, 1:07pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/6 "2021-10-02T13:07:25Z")
Thanks @Beliavsky ---
**Author:** ![urbanjost](https://avatars.discourse-cdn.com/v4/letter/u/0ea827/32.png) [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)\ **Post date:** [October 2, 2021, 1:28pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/7 "2021-10-02T13:28:14Z")
The [Fortran WIki](http://fortranwiki.org/fortran/show/FAQ#array_constructor) discussion on this shows a generic example for INTEGER values, and references a library that handles this in a very general way via the [DISP(3f) procedure](https://dl.acm.org/doi/10.1145/1486525.1486531) ```auto Kristjan Jonasson, Department of Computer Science, School of Science and Engineering, University of Iceland, Hjardarhaga 4, 107 Reykjavik, Iceland (jonasson@hi.is). ``` that is available on-line in several formats and probably handles any way you want to print small matrices in row-column order. It was also an ACM article. There are several github clones of the library. If you are an fpm(1) user I have a clone of that set up for fpm(1) I think I could add to github in a few minutes (have to re-read the licensing to make sure). ---
**Author:** ![Ashok](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ashok](https://fortran-lang.discourse.group/u/Ashok)\ **Post date:** [October 2, 2021, 2:06pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/8 "2021-10-02T14:06:18Z")
Thanks @urbanjost. That would be a great help ---
**Author:** ![shahmoradi](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/shahmoradi/32/3151_2.png) [@shahmoradi](https://fortran-lang.discourse.group/u/shahmoradi)\ **Post date:** [October 2, 2021, 4:15pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/9 "2021-10-02T16:15:35Z")
Here is one that avoids temporary arrays and `transpose()`, ```fortran integer :: i, j real :: Matrix(5,3) = transpose(reshape([( real(i), i = 1, 15 )], shape = [3,5])) write(*,"(*(g0))") ((Matrix(i,j), ", ", j = 1, 3), new_line("a"), i = 1, 5) end ``` ```auto 1.00000000, 2.00000000, 3.00000000, 4.00000000, 5.00000000, 6.00000000, 7.00000000, 8.00000000, 9.00000000, 10.0000000, 11.0000000, 12.0000000, 13.0000000, 14.0000000, 15.0000000, ``` UPDATE: I think I missed an important part of your question: Matrix of unknown size/shape. The above solution assumes a known shape. ---
**Author:** ![urbanjost](https://avatars.discourse-cdn.com/v4/letter/u/0ea827/32.png) [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)\ **Post date:** [October 2, 2021, 4:21pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/10 "2021-10-02T16:21:48Z")
OK; so add these two lines to your fpm.toml file: ```auto [dependencies] M_display = { git = "https://github.com/urbanjost/M_display.git" } ``` * * * put this program into app/confidence\_test.f90 in your fpm project directory to give it a quick test drive: ```fortran program demo_M_display use M_display implicit none integer, parameter :: rk = selected_real_kind(6), n = 3 real(rk) :: a(n,n), b(n,n), x integer i, j, k(5) forall(i=1:n, j=1:n) a(i,j) = exp(real(i+j-1, rk)) b(i,j) = exp(real(i**j, rk)) end forall call disp_set(advance = 'double') call disp('A = ', a) call disp(b) call disp(a(1:2,:),'f0.5') call disp('MATRIX', a, style='UNDERLINE & NUMBER', unit=-3, digmax=4) end program demo_M_display ``` * * * and enter ```bash fpm run confidence_test --profile release --compiler gfortran ``` And you should get just about any form of matrix output you can think of, like: ```nohighlight A = 2.718 7.389 20.086 7.389 20.086 54.598 20.086 54.598 148.413 2.71828E+00 2.71828E+00 2.71828E+00 7.38906E+00 5.45981E+01 2.98096E+03 2.00855E+01 8.10308E+03 5.32048E+11 2.71828 7.38906 20.08554 7.38906 20.08554 54.59815 MATRIX -------------------- 1 2 3 1 2.7 7.4 20.1 2 7.4 20.1 54.6 3 20.1 54.6 148.4 ``` and you can get rid of the confidence\_test.f90 file and just add the “use M\_display” and the call(s) to disp(3f) into your code optionally selecting the options you want and that should do it. I need to clean up the github repository and add more of the original author’s examples and such but that will let you try it. PS: The documentation is on [M\_display](https://github.com/urbanjost/M_display) already. There is a lot of documentation but for basic use you just “call disp(array)”. ---
**Author:** ![Ashok](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ashok](https://fortran-lang.discourse.group/u/Ashok)\ **Post date:** [October 2, 2021, 4:48pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/11 "2021-10-02T16:48:46Z")
Thank you. This is what I am exactly looking for. ---
**Author:** ![urbanjost](https://avatars.discourse-cdn.com/v4/letter/u/0ea827/32.png) [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)\ **Post date:** [October 2, 2021, 6:18pm UTC](https://fortran-lang.discourse.group/t/printing-a-matrix-of-unknown-size-to-file-preserving-the-shape/1985/12 "2021-10-02T18:18:38Z")
No prob. Been meaning to do some fpm(1) wrappings of some other Open Source packages anyway. The more the merrier. I am hoping others will find this useful as well. I would like to merge some other routines with this so one can flip a switch and get the output as a table in CSV, HTML, a few markdown varients, LaTex, … as well. One of these days …