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Origin is a convenient data analysis and graphics program that runs in Windows on PCs. You can use Origin to plot data, transform raw data to more meaningful quantities through column-based calculations, compare data to a theoretical model using linear and nonlinear least-squares fitting, and determine the quantitative agreement between the data and model.
These instructions apply to version 4.0, which is available on the HMC server. Version 3.5 is also available on the server, and differs from 4.0 in several aspects of the user interface. See the documentation on Origin 3.5 for more information.
A quick note on notational conventions in on this page: Text appearing in Bold generally denotes the literal text appearing onscreen. The notation A|B means select item B from menuA.
A sample graph is shown below. Click on an aspect of the graph to learn how to adjust or produce that element in Origin. Beneath the graph is a table of contents of all the topics covered on this page.
This section explains the basic philosphy of Origin, and ends with abrief glossary of the most important Origin terms. The rest of thedocumentation will explain specific Origin features and will make useof Origin terminology.
Origin is built around Windows' Multiple Document Interface (MDI). MDI is a technical standard which allows a single program to create "childwindows" with in its "work area" (the work area is the entire area within the window of an application below its pull-down menu). Each window can be moved and resized independently. Each of Origin's five types of child windows has its own menu structure. The menu visible onscreen will correspond to the type of the active window. To change the active window, you can click on a window to activate it, or you can press Control-Tab to cycle through all open windows. All the windows open on screen constitute a "project," which can be saved and reopened as a unit. If you close a window (as opposed to minimzing it), whatever was in that window is destroyed.
The types of child windows are worksheet, graph, function graph, page layout, and matrix. The primary emphasis of this page is on worksheet and graph windows, as they are of the most interest when plotting real world data. A worksheet is similar to a spreadsheet, and is used for holding data. A graph represents a single logical page and all the plots (called "layers" in Origin) which are on it. A function graph is used to plot mathematical functions. A page layout window, though not covered on this page (maybe in the next version...), is useful as it allows you print different worksheets and graphs on a single piece of paper. A matrix can be used to compute various matrix operations; it is not discussed on this page and is mentioned only for completeness.
You can also paste regularly shaped blocks from any Windows spreadsheet into Origin.
Origin can directly import data from the following binary formats: Excel, Lotus 1-2-3, DBase, and DIF. To import, selectImport|Format-Name.
Use the File|Import|ASCII command to access text files. Many different file configurations can be handled by setting appropriate file import options. For example, to import a tab-delimited text file, do the following:
You can enter values into a column using a formula based on another column.
A data set is placed in a single column. Each Y column is associated with the nearest X column to its left. These associations are indicated by affixing a number after the Y in the column heading. For example, a column marked Y2 is associated with the X2 column. In each layer, you can have multiple X columns and multiple Y columns. Unless you specify otherwise, a Y column will be automatically graphed against its associated X column. In addition, you can have a x and y error columns for each X or Y data set. Once you have entered your data, do the following to create a graph:
The procedure outlined above only works if all your columns are contiguous. If they are not, the following alternate procedure is necessary. Please note that all data sets that form a single data plot must be on the same worksheet.
If you want to change the size of the layer, do it before adding any labels, so that you can pick a font size that fits the graph. There are two ways to adjust the size the layer or move it around on the page. The first is:
The other is:
By default, Origin will put a frame around the plot area only if you plot the scatter type. If you made some other type of graph, you will need to add one. Here's how:
By default, Origin adjusts the range of each axis automatically. You canoverride its choice as follows:
Data points should be plotted as individual points with a symbol size that makes sensefor the number of data points in the plot and the plot size. There should not be a line connecting successive points. Points should be shownwith error bars, if available. Make a column of error bars on your data sheet.
Function graphs are exactly what their name implies: graphs of functions you specify. They are most useful for adding a theoretical curve to a plot of experimental data. The only restriction on the types of graphs is that y must be an explicit function ofx which can be represented using Origin's built-in functions. They can be added as follows:
You may add additional text labels using the text tool ("T" inthe Toolbox) and add lines, with or without arrows, with the line tool. Labels you don't want can be deleted by selecting them and pressingDel. In any text editing box, there are several buttons which can be used to embellish your text:
These may be used in one of two ways. One is to select text already written and then click on the button. The other is to click the button, type your text, and then end the effect by either clicking on Normal or pressing Right-Arrow.
These are some of the most important Greek letters:
Alpha: a. | Beta: b. | Gamma: g. | Delta: d. | Epsilon: e. | Mu: m. | Chi: c. |
Theta: q | Phi: f. | Pi: p. | Nu: n. | Lamba: l. | Omega: w. | Psi: y. |
The method described below makes use of Origin's built in linear regression tool. This has the advantages of being quick and easy, but has the disatvantage of ignoring the uncertainties (errors) in your data. It does not calculate a meaningful c^{2}, so you cannot readily determine how confident you can be of the fit. In general, you should define an appropriate fitting function, as described in Fitting to an Arbitrary Curve.
The result will appear in the Script Window. You will need to enlarge the window and scroll up several lines in order to see it. To enlarge a window in Windows, click on the lower right-hand corner and drag it to the new size. in You can cut and paste the results from there into a text label on the plot as follows:
The arbitrary curve fitter (called NLSF for Nonlinear Least-Squares Fitter) in Origin is both powerful and complex. Consult the Origin manual for a complete description of its capabilities. The following section will simply provide a tutorial for basic operation. The example will be a linear fit function of the form y = mx+ b. This function has two free parameters, namely m andb.
Nonlinear curve fitting is a tricky business. Most often its success rides on choosing initial guesses for the parameters that are close to the best-fit values. If they are too far away, the process may get stuck in a local minimum, unable to find the best fit.
There are four main possibilities that arise when Origin gives you an error message while during LM.
If Origin never settles in a one value of the parameters, then you probably have too many. Try either eliminating some of them or prevent them from being varied by clicking on the Vary? check box inthe Fit window.
For use in a lab notebook, it is very convenient to print a version of your graph that is small enough to permit you to annotate the graph and explain its significance on the same notebook page. A graph with a plot area of about 4 inches by 3 inches is quite good for this.
Left to its own devices, Origin will fill the entire page. This is usually bigger than you want. To shrink it down, click on the lower right corner of the plot area until you get a square drag handle. Resize the plot area until it is the size you want. I do not know of a way to see numerically how large the plot will be, nor a way to type the exact size you want in directly. If you do, please tell me!
Written by Itai Seggev and "PNS".
Copyright © 2001 Harvey Mudd College Physics Department http://www.physics.hmc.edu/ WebMaster@Physics.hmc.edu This page was last modified on Tue, Jan 13, 1998. |