Gnuplot - Revision history

Cclark: /* Plot Display Options */

2013-02-26T15:46:13Z

‎Plot Display Options

Cclark: /* plot Command Modifiers */

2013-02-26T15:12:00Z

‎plot Command Modifiers

Cclark: /* More Sophisticated Data Files */

2013-02-25T19:57:02Z

‎More Sophisticated Data Files

Cclark at 16:42, 21 February 2013

2013-02-21T16:42:37Z

Cclark at 15:55, 21 February 2013

2013-02-21T15:55:13Z

Cclark at 15:40, 21 February 2013

2013-02-21T15:40:46Z

Cclark at 15:39, 21 February 2013

2013-02-21T15:39:58Z

Cclark at 15:35, 21 February 2013

2013-02-21T15:35:51Z

Cclark at 15:21, 21 February 2013

2013-02-21T15:21:05Z

Cclark at 15:11, 21 February 2013

2013-02-21T15:11:39Z

@@ Line 233: / Line 233: @@
    gnuplot> set style data lines       # plot data as lines
    gnuplot> set style data linespoints # plot data as points connected by lines
 ; terminal

@@ Line 166: / Line 166: @@
 ===<code>plot</code> Command Modifiers===
 In its simplest form the plot command just takes a list of functions or files to plot. However, each plot can be ''modified'' by specifying a set of modifiers. The modifiers are just given after the function or file to be plotted. For example, <code>using</code> and <code>every</code> are modifiers that can be applied to data files.
 ===Plot Display Options===

@@ Line 158: / Line 158: @@
   gnuplot> plot 'simple2.txt' using ($1 - 10):2                        # plot column 2 vs column 1, but shift the x axis by 10
   gnuplot> plot 'simple2.txt' using (2*$1):(5*exp( $2 ) )              # plot column 2 vs column 1, manipulating both first
 ===<code>plot</code> Command Modifiers===

@@ Line 152: / Line 152: @@
   gnuplot> plot 'simple2.txt' using 1:(4.5*$3)
-Notice the parenthesis and the $3.
+Notice the parenthesis and the $3. If an integer is given, the integer is taken to be the column number to use. If a calculation involving columns is to be used, it must be enclosed with parenthesis and the columns are refered to with a '$' (similar to gawk). Calculations involving columns can use data from ''any'' column. The using command can be used to do some ''very'' powerful things
 ===Plot Display Options===

@@ Line 148: / Line 148: @@
   gnuplot> plot 'simple2.txt' using 1:3
-The <code>using</code> modifier selects the columns to use in the plot. As expected, the above plot command selects the first and third columns.
+The <code>using</code> modifier selects the columns to use in the plot, but can also be used to manipulate the data ''before'' it is plotted. For example, to multiply all y values by 4.5 and plotting the results,
 ===Plot Display Options===

← Older revision		Revision as of 15:40, 21 February 2013
Line 107:		Line 107:

	[[Media:simple2.txt\|simple2.txt]]		[[Media:simple2.txt\|simple2.txt]]
		+
		+	[[Media:large-data.txt\|large-data.txt]]

	gnuplot reads plain text files in table format: one row per line with columns separated by white space. Each row in the table is used to create ''one'' data point on the graph. The simplest file that gnuplot can read contains just two columns of data points,		gnuplot reads plain text files in table format: one row per line with columns separated by white space. Each row in the table is used to create ''one'' data point on the graph. The simplest file that gnuplot can read contains just two columns of data points,

← Older revision		Revision as of 15:39, 21 February 2013
Line 105:		Line 105:

	[[Media:simple.txt\|simple.txt]]		[[Media:simple.txt\|simple.txt]]
		+
	[[Media:simple2.txt\|simple2.txt]]		[[Media:simple2.txt\|simple2.txt]]

@@ Line 102: / Line 102: @@
 ===Plotting Data from a File===
-gnuplot is very useful for plotting arbitrary functions, but it really shines when it comes to plotting data in a file. gnuplot makes it simple to quickly plot data stored in a plain text file. Typically this has either been generated from a computer model, or collected in an experiment.
+gnuplot is very useful for plotting arbitrary functions, but it really shines when it comes to plotting data in a file. gnuplot makes it simple to quickly plot data stored in a plain text file. Typically this has either been generated from a computer model, or collected in an experiment. Here are two small text files containing data that can be used to follow the examples below.
 [[Media:simple.txt|simple.txt]]
 gnuplot reads plain text files in table format: one row per line with columns separated by white space. Each row in the table is used to create ''one'' data point on the graph. The simplest file that gnuplot can read contains just two columns of data points,
@@ Line 113: / Line 114: @@
 .3  1.9
-gnuplot can plot this file directly,
+gnuplot can plot this file directly. The first column is used for the x coordinates and the second column is used for the y coordinates,
-  gnuplot> plot 'simple.txt'  # note the quote marks
+  gnuplot> plot 'simple.txt'  # note the quotes. single or double quotes can be used
-This turns out to be fairly convenient because it is not very difficult to write code to write files in this format
+  // arrays x and y contain the x and y coordinates of our data
    // C
@@ Line 130: / Line 132: @@
      std::cout<<x[i]<<" "<<y[i]<<std::endl;
-When analyzing data, this is often all that is required to see trends. However, if we are going to show out graph to anybody else, we will certainly want to fix it up.
+=====More Sophisticated Data Files=====
+gnuplot can plot data from files even if there are more than two columns. By default, gnuplot will read the file and use the first two columns and ignore the rest.
   > cat simple2.txt
@@ Line 227: / Line 208: @@
    gnuplot> set terminal jpeg       # write in jpeg format
    gnuplot> set terminal x11        # send plot to X11 (view plot on the screen)
 ; output
 : set name of a file to write output to. this is used together with the <code>terminal</code> option.
-   gnuplot> set terminal png        # write in png format
+   gnuplot> set output "filename.png"        # write in png format
-   gnuplot> set terminal postscript # write in postscript format
+   gnuplot> set output "filename.postscript" # write in postscript format
-   gnuplot> set terminal jpeg       # write in jpeg format
+   gnuplot> set output "filename.jpeg"       # write in jpeg format
 ==Creating Images==

@@ Line 59: / Line 59: @@
 The default plot generated by gnuplot is not bad (the background isn't gray), but unless you are just quickly plotting something for your own use, you will need to change this. For example, you will want to label the axes and indicate their units.
-Gnuplot allows the way the plot is displayed to be configured by setting options. To set options, use the <code>set</code> command
+Gnuplot allows the way the plot is displayed to be configured by setting options. Options are set with the <code>set</code> command
   gnuplot> set title "Displacement of an Oscillating Spring"
@@ Line 65: / Line 65: @@
   gnuplot> set ylabel "displacement (m)"
-Gnuplot does not redraw the graph automatically. To update the plot, either reissue the <code>plot</code> command, or just use the <code>replot</code> command.
+Gnuplot does not redraw the graph automatically after options are set. To update the plot, either reissue the same <code>plot</code> command, or just use the <code>replot</code> command.
   gnuplot> replot  # redraw the previous plot with new options
-See [[#Plot Display Options|this]] section for a list of common options.
+See the [[#Plot Display Options]] section for a list of common options.
 ====User-Defined Functions and Variables====
@@ Line 90: / Line 90: @@
   gnuplot> plot gauss(x, 5, 0)
-gnuplot also also supports variables. You can set a variable, and then use it in plot commands or even function definitions.
+gnuplot also also supports variables. You can set a variable, and then use it in <code>plot</code> commands or even function definitions.
   gnuplot> x0 = 1.5
@@ Line 98: / Line 98: @@
 This function will use the values stored in <code>x0</code> and <code>sigma</code> when it is evaluated. Note that the <code>x0</code> and <code>sigma</code> in the function <code>gauss</code> defined above will '''not''' use the variables. Function argument names will "hide" variable names. In other words, gnuplot variables have ''scope''.
-  gnuplot> plot gauss(0.5, 1, x), gauss2(x)
+  gnuplot> plot gauss(0.5, 1, x), gauss2(x), gauss2(x/sigma)
 ===Plotting Data from a File===
-We often need to plot data that is stored in a file. Typically this has either been generated from a computer model, or collected in an experiment. gnuplot has a very powerful set of utilities for plotting data from a file. The data files used in the examples that follow can be downloaded here.
+gnuplot is very useful for plotting arbitrary functions, but it really shines when it comes to plotting data in a file. gnuplot makes it simple to quickly plot data stored in a plain text file. Typically this has either been generated from a computer model, or collected in an experiment.
 [[Media:simple.txt|simple.txt]]

@@ Line 52: / Line 52: @@
   gnuplot> plot sin(x)
-Note that <code>x</code> is a special variable that gnuplot reconizes as the independent variable. Multiple functions can be plotted on the same graph, just separate each with a comma
+Multiple functions can be plotted on the same graph, just separate each with a comma
   gnuplot> plot sin(x), cos(x)