I have made my own set of routines for scientific 2D and 3D line, surface and color plotting, based on the familiar MATLAB plotting commands and addopted a simple subset of these for use by students. These are placed in the module SimpleGraphics. Take a look at the source file with the Fortran 90 module to see exactly what I did if you are interested. Examples are given at the bottom of this page.

The module provides several routines. Here I give their interface and an explanation of how they are used. The examples given after that will make everything much clearer:

• The subroutine InitGraphics must be called to initialize the graphics environment before any plotting routines:

SUBROUTINE InitGraphics(file,file_type,plot_title,x_label,y_label,z_label)
   CHARACTER(*), OPTIONAL, INTENT(IN) :: file,file_type
   CHARACTER(*), DIMENSION(:), OPTIONAL, INTENT(IN) :: plot_title
   CHARACTER(*), OPTIONAL, INTENT(IN) :: x_label,y_label,z_label
END SUBROUTINE InitGraphics

Notice that all of its arguments are optional, although a meaningful plot should have all of them defined. The string file gives the name of the file to which the created image will be written (if the image is displayed on screen, no file is really created). The most important argument is the string file_type which defines what kind of an image file is produced. Most often  used are "CONS" for the whole X screen (no file is written), "POST" for PostScript (.ps) files (for printing), "JAVA" for Java applets, "PNG" for PNG images, etc.
The axis labels for the x, y and z (if present) axis, x_label, y_label and z_label, are also simple strings. The title of the plot plot_title should be an array of strings, one string for each line in the title. Note that this is most easly done using array constructors, as in,
plot_title=(/"Line 1","Line 2"/)
however, this does not work with f90-vast due to some internal bug. See the examples below for proper usage.
• The subroutine EndGraphics must be called to end the graphics environment and write the output to the file:

SUBROUTINE EndGraphics()
END SUBROUTINE EndGraphics

NOTE: To close the DISLIN X window with the plot (opened with "CONS"), click the left or middle mouse button.
• The subroutine AddLegend can be used to add a legend to a plot if that is needed:

SUBROUTINE AddLegend(legends,position)
   CHARACTER(*), DIMENSION(:), INTENT(IN) :: legends
   INTEGER, OPTIONAL, INTENT(IN) :: position
END SUBROUTINE AddLegend

It takes the array of strings legends with one string for each line in the legend (i.e. for each curve) and optionally the integer position of the legend position (3 and 7 are most used--upper right corner of page and upper right corner of plot) as argumens.
• The subroutine Plot2D is the main routine for plotting curves with points on two dimensional plots. It can be called several times in a row to plot several curves on the same plot. Its somewhat complicated interface is:

SUBROUTINE Plot2D(x,y,plot_spec,new_plot,axis)
   REAL, DIMENSION(:), INTENT(IN), OPTIONAL :: x
   REAL, DIMENSION(SIZE(x)), INTENT(IN), OPTIONAL :: y
   CHARACTER(LEN=3), OPTIONAL, INTENT(IN) :: plot_spec
   LOGICAL, OPTIONAL, INTENT(IN) :: new_plot
   REAL, DIMENSION(4), OPTIONAL, INTENT(IN) :: axis
END SUBROUTINE Plot2D

The single-precision real vectors of equal size x and y contain the data points to be plotted. The optional single-precision vector of 4 values axis gives the axis limits. If it is not present, the routine will choose the axis limits so as to fit the whole range of x and y values. For example, use axis=(/x_min,x_max,y_min,y_max/).
An important argument is the logical indicator new_plot, which tells the routine whether we are making a brand new plot (i.e. this is the first call to Plot2D) or we are adding a curve to a plot that was already started. The default is new_plot=.TRUE..  Usually it is not wise to give an axis specification with new_plot=.FALSE., since this will overwrite previous axis.  Although it is possible to have the routine keep track of this itself, this gives more freedom to the user to achive special effects such as overlapped plots with different axis.
The three-character specification string plot_spec determines the curve attributes and thus how the plot actually looks. The specification string has the following interpretation:
1. The first character should be one of 'S' (plot data points as symbols--no line), or 'L' (plot data points connected with a line--no symbols). If you want both a line and symbols, call the routine twice with the same data but different specification.
2. The second character for symbol plots (i.e first specification character was 'S') plots should be on of 'S' (use squares as symbols), 'C' (circles), 'T' (triangles), 'D' (diamonds), or lower-case letters ('s' 'c' 't' 'd') for the corresponding filled symbols (filled squares, filled circles, filled triangles and filled diamonds).

For line plots (i.e first character was 'L'), the second character should be one of '-' (solid line), '.' (dotted), ':' (dashed) or '|' (dashed-dotted).
3. The third character determines the color of the curve and should be one of 'R' (red), 'B' (blue), 'G' (green) or 'Y' (yellow).
For example, an argument plot_spec="STR" will plot the data points as symbols using red triangles, while plot_spec="L-G" will connect the data points with a green solid line. Here is a typical call to Plot2D:
CALL Plot2D(x=x_data,y=y_data,plot_spec="L-G",new_plot=.TRUE.,axis=(/x_min,x_max,y_min,y_max/))
• The subroutine Plot3D is the main routine for plotting curves with points in three dimensions dimensional. It is called in exactly the same way as Plot2D, with an optional parameter specifying the view explained further below, and extra info about the z coordinates and axis:

SUBROUTINE Plot3D(x,y,z,plot_spec,new_plot,axis,view)
   REAL, DIMENSION(:), INTENT(IN), OPTIONAL :: x
   REAL, DIMENSION(SIZE(x)), INTENT(IN), OPTIONAL :: y,z
   CHARACTER(LEN=3), OPTIONAL, INTENT(IN) :: plot_spec
   LOGICAL, OPTIONAL, INTENT(IN) :: new_plot
   REAL, DIMENSION(6), OPTIONAL, INTENT(IN) :: axis
   REAL, DIMENSION(3), OPTIONAL :: view
END SUBROUTINE Plot3D

• Two main types of three dimensional plots are often used, surface plots, in which a third dimension is emulated with possibly coloring to give the value of a function z=f(x,y), or color plots, in which the plot is two dimensional but color is used to denote the magnitude of f(x,y). These kinds of plots can be made with the subroutine SurfPlot, which is somewhat more advanced. It should not be used to put more than one plot on the same graph, since this is somewhat of a difficult task:

 SUBROUTINE SurfPlot(x,y,z,plot_spec,color_range,axis,view) 
   REAL, DIMENSION(:), INTENT(IN) :: x,y
   REAL, DIMENSION(SIZE(X),SIZE(Y)), INTENT(IN) :: z
   CHARACTER(3), OPTIONAL, INTENT(IN) :: plot_spec
   REAL, DIMENSION(2), OPTIONAL, INTENT(IN) :: color_range
   REAL, DIMENSION(6), OPTIONAL, INTENT(IN) :: axis
   REAL, DIMENSION(3), OPTIONAL, INTENT(IN) :: view
 END SUBROUTINE SurfPlot

It accepts the same kind  of arguments as Plot2D, with additional optional 2/3 element arrays specifying the camera position view (in polar (phi,theta,r) coordinates--angles as degrees, not radians!) and color range color_range (the largest and smallest representable magnitudes), which are usually chosen well automatically. The specification string plot_spec has the following interpretation in this case:
1. The first character should be one of '2' (plot data points as a 2D color plot), or '3' (plot data points as a 3D surface).
2. The second character for color ('2') plots should be a digit from 1-9 and specify the increase in the resolution (number of linear-interpolation interior-points). For surface ('3') plots, this character should be one of 'M' (mesh line surface), 'C' (color-shaded surface) or 'S' (both mesh and color shading).
3. The third character determines the color palette and should be one of 'R' or 'r' (rainbow palette in two different directions of hot-cold), 'G' or 'g' (gray palette in two different directions) or 'V' (VGA 16 color palette).