How can i use gnuplot

Open your text editor, then cut and past the following into it. The indicates a comment line. Any line starting with will be ignored by gnuplot. Save this file to your current directory as example. Undergraduate Physics Laboratories GO.

GNUplot Tutorial Gnuplot is an open-source command-line program. To save the current setting, use save command followed by a file name in which parameters and functions you defined are stored. The file name is quoted by a single or double quotation.

The file name is arbitrary, but if the same name exists in the current directory, gnuplot overwrites internal parameters in that file without any warnings. The saved file is a usual text file. You can edit the contents with a text editor. To draw a graph again with this file, use the load "savefile. If you give the data-file name as a command line option the second case , gnuplot ends after it reads the file, and you come back to shell.

This is a batch mode. There are two basic commands to plot a graph, plot and splot. The former is used for a 2-dimensional graph, and the latter is for a 3-dim. Gnuplot makes a graph of any kinds of functions or numerical data stored in a file. You can omit the range parameters.

This is the 2-dimensional graph gnuplot generates. The frame is drawn by a thick line, which is called "border". The X and Y axes have graduation called "major tics", and numeric labels are written at the tics location.

The intervals between each major tic can be divided by minor tics. You can draw names of X and Y axes. GNUPlot is an actively developed freely distributed non-open source command line graphing and plotting software tool that was initially released back in GNUPlot can be useful for a wide spectrum of applications, so here comes a quick guide that will help you understand how it works, get to play with its basic functionality, and learn how to take your first steps with it the easy way.

This will launch the software tool so you are ready to set your variables and start plotting. Note that GNUPlot warns me that I have not defined a value range for my graph so it has automatically assigned one for me. If I want to do this myself, I can define a specific range by adding two numbers separated by a colon inside square brackets as shown in the following screenshot. To do this, type.

After learning how to plot functions, now it's time to learn how to plot data. The syntax is almost the same, except that instead of specifying a function, you must specify the name of the file containing the data to plot, enclosed in double quotes. First, since we were playing around with plots above, we'll clear the labels on the axes and other settings:. You could also quit gnuplot and restart it for the same effect.

Now, we'll plot our sample data. We'll get rid of an entry in the legend for our data points by using a title of "" , and also set up the axes on the plot:. When plotting data, it usually isn't necessary to specify ranges for the independent and dependent variables, since they can be figured out from the input.

If necessary, of course, you can always give them. Since our input data contains uncertainties for the measured dependent quantity, we can create y error bars. Once again, gnuplot makes this easy:. It's possible to plot x error bars using xerrorbars , or both x and y errorbars using xyerrorbars. When both x and y error bars are used, there must be four columns present, and x error bars must be specified first in the data file.

More variations are possible; see the online help for more information. Note that gnuplot can be very picky about the order you give modifiers to the plots. If you were instead to type. You'd get a rather strange error message: undefined variable: title.

If you see error messages like this, check the ordering in your plot commands. If you're unsure, typing help plot should get you straightened out. No plotting program would be complete without the ability to fit our data to a curve. For the Cavendish experiment, we'll need to fit our data to a sinusoidal curve with exponential decay. First, it's necessary to define the form of the function we'll try to fit to. Define this as you would any other function in gnuplot, but leave variables for the fitting parameters.

We'll use. For a non-linear curve fit such as this, it is often necessary to provide an initial guess for each of the fitting parameters, or the fitting attempt may fail. For simple equations, such as polynomials, this will not be necessary but never hurts. Here's how the command is interpreted: fit tells gnuplot we're doing a curve fit. The next part, theta x , must be a function that we're using to fit the data. Here we must use x as the independent variable.

The next part, "cavendish. The using tells gnuplot to take columns 1, 2, and 3 from the data file and use them as the x, y, and uncertainties, respectively. If this part is left out, then the experimental uncertainties will not be used for the curve fit.