HomeHow do I...?KaleidagraphFitting ExerciseOrigin 3.5 • Origin 4.0 • Lab Note Books

Using Origin 4.0 on the PC

Linear fit information Plotting Data Axes

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.

Sample Plot

Introduction and Glossary up picture

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.


Child Window:
One of the windows within the Origin work area. There are five types of child windows: worksheet, graph, matrix, page layout, and function graph. The menus available depend on which type the active window is.
A graphical representation of data. Typically composed of several data sets (x data set, y datset, error data sets).
Data set:
A collection of data points in a single column of a worksheet.
A child window containing plots. Each plot is in a layer, and a single graph window can have up to fifty layers.
A graphical object composed of a set of x and y axes, one or more data plots, and associated text and graphical labels.
A collection of child windows which can be saved at reopened as a unit.
The toolbar which is visible when you first start Origin.
A spreadsheet-like child window in which you can enter data sets in columns.

Entering Data up picture

You have several options for entering data into Origin. If your data have not yet been entered into the computer, you may type them into an Origin worksheet. If they already exist in a text file or in one of a number of binary files, you can use Origin's Import ... command to read the data into an Origin worksheet. If they are available in another program whose fileformat is not supported, most programs will allow you to export the file as tab-delimited ASCII (or other ASCII formats) which you can import. For Excel or other Windows programs, you can also use cut-and-paste between them.

Keyboard Entry up picture

Type your data in columns noting the following points:

Cut and Paste up picture

You can also paste regularly shaped blocks from any Windows spreadsheet into Origin.

  1. Go into your spreadsheet and select your data.
  2. Select Edit|Copy or press Control-C.
  3. Press Alt-Tab until you reach Origin.
  4. Click on the upper left hand corner of where you want to paste the block.
  5. Select Edit|Paste or press Control-V.

Import from a Non-Origin File up picture

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:

  1. Select File|Import|ASCII Options
  2. From the Delimeted, Delimeter pop-up menu choose Tab
  3. Click on Import Now
  4. Select the file and click on OK.

Using a Formula up picture

You can enter values into a column using a formula based on another column.

  1. Select the column into which you want to enter the results by clicking on the column name.
  2. Choose Data|Set Column Values
  3. Enter the formula you want to use in the text box. Useful functions include:
    • col(x): returns the value in column x. Note: x is the name of the column.
    • log(x): common log of x.
    • x^y: x raised to the y power.
    • sin(x), cos(x), tan(x): your everyday trig functions.
    • asin(x), acos(x), atan(x):inverse trig functions.
    • NOTE: all trig functions work in radians by default.
  4. Set the rows for which you want this formula to apply (upper right-hand corner).
  5. Click on Do It.

Plotting Data up picture

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:

Plotting Adjacent Data sets up picture

  1. Select the column holding the x data.
  2. Choose Column|Set as X.
  3. In place of the previous two steps, you can double click on the column heading a select X from the Set Column As pop up menu.
  4. If you have a (several) column(s) of errors:
    • Select the column(s).
    • Choose the command Column|Set as Error Bars (or choose Err Bars after double clicking on the column heading.)
    • For x error column, you will need to also choose Column|Error Bar Options and click on X error bar.
  5. Select the x, y, and errors columns.
  6. Choose the command Plot|Scatter.
  7. It may be useful at this point to expand the window by clicking the up arrow at the right of the title bar.

Plotting Non-Adjacent Data sets up picture

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.

  1. Without any columns selected, choose Plot|Scatter.
  2. Single click on the name of the column you want to hold the xdata.
  3. Click on the X button.
  4. Repeat this process for Y, yEr, and xEr.
  5. Click on the Add button.
  6. Repeat steps 2-5 for each y column. The x columnsneed not be the same.
  7. If you want to remove a dataplot from the list of dataplots to bemade , single click on it and then click on the Remove button.
  8. Click on OK.

Resizing and Moving the Plot Layer up picture

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:

  1. Double click on the gray plot-layer button in the upper left-handcorner.
  2. Click on Layer Properties.
  3. Enter new values of the height, width, left, and top.
  4. Click on OK, then click on the new OK.

The other is:

  1. Single click on a corner of the axes. They should change color,and eight control points should appear (one at each corner and the bisections of the sides).
  2. To move the layer, click anywhere inside the axes a drag it to its new location.
  3. To resize the layer, click on one of the control points and drag to a new size. The control points in the corner can be used to adjust the size both horizontally and vertically, while the control points at the bisections can only change the size in the direction perpendicular to the side.
  4. When finished, single click anywhere outside the layer but still on the page. The old plot will now disappear, and a new one will materialize within the box.

Adjusting the Axes up picture

Adding a Box Around the Plot Area up picture

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:

  1. Bring up the x axis diaglog box by either double clickingon the axis or choosing Format|Axes|X Axis
  2. Enable the following check boxes
    • Axis Top
    • Top Axis In (Major)
    • (If you wish) Top Axis In (Minor)
  3. Click the Goto Y button.
  4. Enable the following check boxes by clicking on them.
    • Axis Right
    • Right Axis In (Major)
    • (If you wish) Right Axis In (Minor)
  5. Click on OK

Adjusting the Scale up picture

By default, Origin adjusts the range of each axis automatically. You canoverride its choice as follows:

  1. Double click on the x or y axis, or choose Format|Axes|X Axis or Format|Axes|Y Axis
  2. Enter a new value for the lower bound.
  3. Press Tab and enter a new value for the upper bound.
  4. You may want to adjust Increment, the distance between two consecutive tick marks or enter the number of tick marks directly.
  5. If desired, click on Goto X or Goto Y and repeat this procedure.
  6. Click on OK when finished.

Fixing the Plot Symbols up picture

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.

Turning off lines and/or modifying plot symbols

Adding a function graph up picture

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:

  1. Select Plot|Add Function Graph
  2. Enter the function in the edit area.
  3. Select other options as desired and click on OK

Annotatingthe Graph up picture

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.

FittingData up picture

Fittingto a Line up picture

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 c2, 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.

  1. If the linear regression tool bar isn't visible, selectTools|Linear Fit.
  2. Make surethe data set you want to analyze is the active data set. You can do so by selecting the Data. There will be anX next to the active data set. If the data set is inactive, then click on it or press the underlined number to its left.
  3. Click on the Settings tab.
  4. Make sure that the Span X Axis box is checked.
  5. If desired, check the Residual Data box. This will create a residuals column in the worksheet, which will make it easier to calculate Chi2.
  6. Click on the Operation tab.
  7. Check the the Error as Weight box.
  8. If desired, check the Through Zero box. This forces the line to pass through the origin.
  9. Click on Fit

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:

  1. Make sure there is already a text label for the text to go to, or click on T in the Toolbox to create a new one.
  2. Select the text with in the script window, and chooseEdit|Copy or press Control-C.
  3. Double click on the text label to open it.
  4. Single click within the text edit area to de-select the text. This prevents that text from being destroyed when you paste.
  5. Position the cursor where you want to insert the text.
  6. Select Edit|Paste orpress Control-V.

Fitting to an Arbitrary Curve up picture

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.

  1. Choose Analysis|Non-linear Curve Fit.
  2. Choose Function|New or click on the button with a whitepeace of paper with just f(x) on it. When you quit Origin, it will ask you if you want to save your new function. Choose Discard All.
  3. Check the User-defined Names box.
  4. Click in the Parameter Names box (alternatively, pressTab) and typem,b.
  5. Click in the large equation box at the bottom and type the equation m*x+b. In general, you may use any of the functions listed above in defining your fit function.
  6. Choose Action|Data set or click on the button with with a matrix on it.
  7. In the Data sets box, single click on the data set you want to be the y data and click on Assign.
  8. Choose Options|Control or click on the button with a marionette on it.
  9. From Weighting Method, select Instrumental. This means it will take into account your y-error column when doing the fit.
  10. Choose Action|Fit or click on the button with a green light on it.
  11. At this point, you will need to set initial values for the parameters. Click in each box and enter the value you expect the parameter to be.
  12. Click on 10 Iter.. If the fit goes less than a full ten rounds (the display will tell you how many rounds it completes) then you're done. Otherwise, click on it again. If you receive an error message or if the parameters never stop changing, see NumericalNote below.
  13. Click on Done!. The curve will be plotted, and the results will appear in a text box on the plot.
  14. Double click on the text box, and choose Black Line fromthe Show Background drop-down menu.
  15. NOTE: the value of c2 is really c2 per degree of freedom.

Numerical Note up picture

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.

  1. The function was entered incorrectly. For example, "mx" insteadof "m*x." Choose Function|Edit to correct the mistake.
  2. The original parameters given were so far from the target the LM iterations headed in the wrong direction, eventually causing numeric overflow. Try entering different starting values.
  3. The function being fit is discontinuous. This mainly occurs with trigonometric functions. LM only works with differentiable functions. You will need to change your data in such away as to make the function continuous.
  4. The fitting involves either very large or very small numbers. The LM method is overly gross in the changes it makes, and the function heads of in the wrong direction. This can be corrected by constraining the variables to certain ranges. Choose Options|Constraints.

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.

Printing Graphs up picture

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".

logo picture
Copyright © 2001 Harvey Mudd College Physics Department
This page was last modified on Tue, Jan 13, 1998.