25.4: Example

Last updated
Save as PDF

Page ID: 54409

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

This section provides an example program that plots a simple function.

\[ y = \sin(x) \cdot \left( \frac{1 - \cos(x)}{3.0} \right) \nonumber \]

The program, data file, and final output are presented for reference.

Plot Program

The following is an example program that generates points, opens a plot file, write the header, data points, and footer.

program plotExample

implicit none
real, dimension(200) :: x, y
integer :: i, opnstat

! Generate x and y points
    do i = 1, 200
        x(i) = i * 0.05
        y(i) = sin(x(i)) * (1-cos(x(i)/3.0))
    end do

! Output data to a file
    open (12, file="data.plt", status="replace",        &
                action="write", position="rewind",      &
                iostat=opnstat)
    if (opnstat > 0) stop "error opening plot file."

! Write header
    write (12, '(a)') "# Example Plot File"
    write (12, '(a)') "set title ""Example Plot Function"" "
    write (12,'(a,a)') "plot ""-"" notitle with dots ",
                        "linewidth 2 linecolor 2"

! Write points to file.
    do i=1,100
        write (12,*) x(i), y(i)
    end do

! Write footer and close file
    write (12, '(a)') "end"
    write (12, '(a)') "pause -1"
    
    close(12)

end program plotExample

The data file name can be changed or read from the user.

Plot File

The output file from this program appears as follows:

# Example Plot File
set title "Example Plot Function"
plot "-" notitle with dots linewidth 2 linecolor 2
  5.0000001E-02  6.9413913E-06
  0.1000000      5.5457884E-05
  0.1500000      1.8675877E-04
  0.2000000      4.4132397E-04
  0.2500000      8.5854460E-04
  
    [many points not displayed due to space considerations]
  
  4.900000       -1.043852
  4.950000       -1.048801
  5.000000       -1.050716
end
pause -1

The output file can be edited with a standard text editor. This will allow checking the data file for possible errors if it does not display correctly.

Plot Output

The plot output is as follows:

On Windows machines, the plot can be printed by right clicking on the blue bar (on top). This will display a menu, with “Print” as one of the options.