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!      $Id: x04f.f90 11717 2011-04-21 00:47:06Z airwin $
!      Illustration of logarithmic axes, and redefinition of window
!
!      Copyright (C) 2004  Alan W. Irwin
!
!      This file is part of PLplot.
!
!      PLplot is free software; you can redistribute it and/or modify
!      it under the terms of the GNU Library General Public License as
!      published by the Free Software Foundation; either version 2 of the
!      License, or (at your option) any later version.
!
!      PLplot is distributed in the hope that it will be useful,
!      but WITHOUT ANY WARRANTY; without even the implied warranty of
!      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
!      GNU Library General Public License for more details.
!
!      You should have received a copy of the GNU Library General Public
!      License along with PLplot; if not, write to the Free Software
!      Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

      use plplot
      implicit none

!      Process command-line arguments
      call plparseopts(PL_PARSE_FULL)

      call plinit
      call plfont(2)
!      Make log plots using two different styles.
      call plot1(0)
      call plot1(1)
      call plend
      end

      subroutine plot1(type)
      use plplot, PI => PL_PI
      implicit none
      real(kind=plflt)  freql(0:100),ampl(0:100),phase(0:100), freq, f0
      integer           i, type
      integer           nlegend

      real(kind=plflt)  legend_width, legend_height
      integer           opt_array(2), text_colors(2), line_colors(2), &
                        line_styles(2), line_widths(2), symbol_colors(2), &
                        symbol_numbers(2)
      real(kind=plflt)  symbol_scales(2), box_scales(0)
      integer           box_colors(0), box_patterns(0)
      integer           box_line_widths(0)
      character(len=20) text(2)
      character(len=1)  symbols(2)

      call pladv(0)
!      Set up data for log plot.
      f0 = 1._plflt
      do i=0,100
        freql(i)= -2.0_plflt + dble (i)/20.0_plflt
        freq=10.0_plflt**freql(i)
        ampl(i)=20.0_plflt*log10(1.0_plflt/sqrt(1.0_plflt+(freq/f0)**2))
        phase(i)=-(180.0_plflt/PI)*atan(freq/f0)
      enddo
      call plvpor(0.15_plflt, 0.85_plflt, 0.1_plflt, 0.9_plflt)
      call plwind(-2.0_plflt, 3.0_plflt, -80.0_plflt, 0.0_plflt)
      call plcol0(1)
!      Try different axis and labelling styles.
      if (type.eq.0) then
        call plbox('bclnst', 0.0_plflt, 0, 'bnstv', 0.0_plflt, 0)
      elseif (type.eq.1) then
        call plbox('bcfghlnst', 0.0_plflt, 0, 'bcghnstv', 0.0_plflt, 0)
      else
        stop 'plot1: invalid type'
      endif
!      Plot ampl vs freq.
      call plcol0(2)
      call plline(freql,ampl)
      call plcol0(2)
      call plptex(1.6_plflt, -30.0_plflt, 1.0_plflt, -20.0_plflt, 0.5_plflt, &
                  '-20 dB/decade')
!      Put labels on.
      call plcol0(1)
      call plmtex('b', 3.2_plflt, 0.5_plflt, 0.5_plflt, 'Frequency')
      call plmtex('t', 2.0_plflt, 0.5_plflt, 0.5_plflt, &
                  'Single Pole Low-Pass Filter')
      call plcol0(2)
      call plmtex('l', 5.0_plflt, 0.5_plflt, 0.5_plflt, 'Amplitude (dB)')
      nlegend = 1
!      For the gridless case, put phase vs freq on same plot.
      if(type.eq.0) then
        call plcol0(1)
        call plwind(-2.0_plflt, 3.0_plflt, -100.0_plflt, 0.0_plflt)
        call plbox(' ', 0.0_plflt, 0, 'cmstv', 30.0_plflt, 3)
        call plcol0(3)
        call plline(freql, phase)
        call plstring(freql, phase, '*')
        call plcol0(3)
        call plmtex('r', 5.0_plflt, 0.5_plflt, 0.5_plflt, &
                    'Phase shift (degrees)')
        nlegend = 2
      endif

!     Draw a legend
!     First legend entry.
      opt_array(1)   = PL_LEGEND_LINE
      text_colors(1) = 2
      text(1)        = 'Amplitude'
      line_colors(1) = 2
      line_styles(1) = 1
      line_widths(1) = 1
!     note from the above opt_array the first symbol (and box) indices
!     do not have to be specified

!     Second legend entry.
      opt_array(2)      = PL_LEGEND_LINE + PL_LEGEND_SYMBOL
      text_colors(2)    = 3
      text(2)           = 'Phase shift'
      line_colors(2)    = 3
      line_styles(2)    = 1
      line_widths(2)    = 1
      symbol_colors(2)  = 3
      symbol_scales(2)  = 1.0
      symbol_numbers(2) = 4
      symbols(2)        = '*'

!     from the above opt_arrays we can completely ignore everything
!     to do with boxes. (Hence the size 0 for the associated arrays)
!     (note: use the argument nlegend explicitly)

      call plscol0a( 15, 32, 32, 32, 0.70_plflt )
      call pllegend( legend_width, legend_height, &
          PL_LEGEND_BACKGROUND + PL_LEGEND_BOUNDING_BOX, 0, &
          0.0_plflt, 0.0_plflt, 0.1_plflt, 15, &
          1, 1, 0, 0, &
          nlegend, opt_array, &
          1.0_plflt, 1.0_plflt, 2.0_plflt, &
          1.0_plflt, text_colors, text, &
          box_colors, box_patterns, box_scales, box_line_widths, &
          line_colors, line_styles, line_widths, &
          symbol_colors, symbol_scales, symbol_numbers, symbols )

      end