如何在Gnuplot上以对数刻度设置部分x轴？

Question

我想绘制一些需要 [2-30] 之间的对数刻度 x 轴和 [30-2500] 之间的常规线性 x 轴的图。

这是我想要的图，x轴是部分对数的。

有人可以帮助我吗？预先感谢您。

编辑：固定范围，添加参考图片。

Answer 1

除了用

nonlinear

“搞乱”之外，另一个选择可能只是将你的图分割成一个包含 4 个子图的多图。 像这样的进一步调整...

脚本：

### split log/lin plots
reset session

mySplitX = 0.33  # split point of log/lin in screen coordinates
mySplitY = 0.33  # split point of upper/lower plots in screen coordinates
myLeftMargin = 10
myRightMargin = 4

unset key
set samples 200
set multiplot
    set border 7
    set origin 0,mySplitY
    set size mySplitX,1-mySplitY
    set margins myLeftMargin, 0, 0, -1   # l,r,b,t
    unset xlabel
    set format x ""
    set mxtics 10
    set logscale x
    set xrange [1:30]
    set ylabel "my y-axis title"
    set ytics nomirror
    set mytics 5
    set yrange [0:6000]
    plot (2500*sin(x)+3000)
            
    set arrow 1 from screen mySplitX, graph 0 to screen mySplitX, graph 1 nohead dt 3
    set border 13
    set origin mySplitX,mySplitY
    set size 1-mySplitX,1-mySplitY
    set margins 0, myRightMargin, 0, -1   # l,r,b,t
    set xlabel " "
    set mxtics 5
    unset logscale x
    set xrange [30:2500]
    unset ylabel
    unset ytics
    set y2tics
    set my2tics 5
    set format y2 ""
    replot 
    
    set border 7
    set origin 0,0
    set size mySplitX,mySplitY
    set margins myLeftMargin, 0, -1, 0   # l,r,b,t
    set xlabel "my x-axis title"  center offset 28,0
    set logscale x
    set xrange [1:30]
    set format x "%g"
    set xtics
    set xtics add (30)
    set mxtics 10
    set ylabel "my Y-label"
    set yrange [-750:750]
    set ytics 300 nomirror
    unset y2tics
    plot (500*cos(x))
    
    set border 13
    set origin mySplitX,0
    set size 1-mySplitX,mySplitY
    set margins 0, myRightMargin, -1, 0   # l,r,b,t
    set xlabel " "
    unset logscale x
    set xrange [30:2500]
    set mxtics 5
    unset ylabel
    unset ytics
    set y2tics 30 nomirror
    set y2range[-75:75]
    set format y2 "%g"
    set my2tics 4 
    plot (50*cos(x)) axis x1y2
    
unset multiplot
### end of script

结果：

补充：

“秘密”只是设置多图的边距和大小，使其看起来像一张图，但具有不同的比例。 在 gnuplot 中检查

help margins

、

help origin

、

help size

。您基本上可以检查每个关键字

help <keyword>

并获得有用的信息。

x 标签仅在第一个图中设置，并带有偏移量 (

help offset

)。

set xlabel "my x-axis title"  center offset 28,0

在第二个图中，它只是一个空白区域。

set xlabel " "

脚本：

### split log/lin plots
reset session

mySplitX = 0.33  # split point of log/lin in screen coordinates
unset key
set samples 200

set multiplot
    set border 7        # show border at bottom,left,top
    set origin 0,0
    set size mySplitX,1
    set margins -1, 0, -1, -1   # left,right,bottom,top
    set xlabel "my x-axis title"  center offset 28,0
    set format x "%g"
    set mxtics 10
    set logscale x
    set xrange [1:30]
    set ylabel "my y-axis title"
    set ytics nomirror
    set mytics 5
    set yrange [0:6000]
    plot (2500*sin(x)+3000)
    
    set arrow 1 from screen mySplitX, graph 0 to screen mySplitX, graph 1 nohead dt 3
    set border 13           # show border at top,right,bottom
    set origin mySplitX,0
    set size 1-mySplitX,1
    set margins 0, -1, -1, -1   # l,r,b,t
    set xlabel " "
    set xtics add (30)
    set mxtics 5
    unset logscale x
    set xrange [30:2500]
    unset ylabel
    unset ytics
    set y2tics
    set my2tics 5
    set format y2 ""
    replot 
    
unset multiplot
### end of script

结果：

添加 2：（使用

set nonlinear

的替代解决方案）

实际上，如果您进行坐标转换，您可以使用

set nonlinear

来简化操作（检查

help nonlinear

）。这样做的优点是避免了

multiplot

，允许在交互式终端中放大。

脚本：

### split graph in log/lin-parts via "set nonlinear"
reset session

### create some test data
set table $Data
    set samples 100
    plot '+' u (x0=10**(log10(30/0.1)/100*$0+log10(0.1))):(sin(0.01*x0)) w table, \
         '+' u (x0=$0*(2500-30)/100+30):(sin(0.01*x0)) w table
unset table

xmin   = 0.1       # "visible" x-minimum
xsplit = 30        # where to split the graph
xmax   = 2500
split  = 0.25      # graph ratio of lower log-part

xRangeH = (xmax-xsplit)*split/(1-split)   # "hidden" lower x-range
xminH   = xsplit - xRangeH                # "hidden" lower x-minimum
decades = log10(xsplit/xmin)

f(x) = x<xsplit ? xRangeH/decades*(log10(x/xmin)) + xminH : x
g(x) = x<xsplit ? 10**((x-xminH)/xRangeH*decades )*xmin   : x

set xrange[xminH:xmax]
set xtics 500
set mxtics 5
set xtics scale 1,1 add ("0.1" 0.1, "1" 1, "10" 10, "30" 30, "200" 200)
set nonlinear x via f(x) inverse g(x)
set grid x,y
set arrow 1 from xsplit, graph 0 to xsplit, graph 1 lc "blue" dt 2 lw 1.5 nohead

plot $Data u 1:2 w lp pt 7 lc "red" notitle
### end of script

结果：