Graph: Basic Usage

Here we describe graphing a dataset. We assume that the files containing the variable names and the data itself have been selected from, say, the File Selection system: the document describing the usage of this system may be found here.

There are two main screens to the interface:

1. The Setup Screen
2. The Graph Screen

The Setup Screen

Selecting the Variables

Let us assume that the dataset contains three variables, which you have named temp, voltage, and errVoltage: we shall not make any assumptions about what these variables may be, although the names are somewhat suggestive.

The first step is to tell the grapher which variables correspond to the dependent variable, independent variable, etc. to be used in the graph. In a graph, the "independent variable" is the one that is graphed on the horizontal axis, and the "dependent variable" is graphed on the vertical axis. the screen to do this selection looks like this:

We shall choose the dependent variable to be voltage whose error is errVoltage; the independent variable is temp and we shall assume that the error in the temperature is zero.

The easy way to do this is to click on the variable names corresponding to the dependent and independent variables of the graph and their corresponding errors. You may also type directly in the blank fields in the line that begins with:

Notice that there is a button labelled DataPoint in the list of possibilities for the independent variable. This will use the line number in the data file as the value of the independent variable. When you click on this button, if there is no value for the error in the independent variable, it will be set to zero. If there is already a value for the error in the independent variable it will not be changed.

Either way, when we are done this part of the Setup screen looks like this:

Because of the meaning of independent and dependent in describing variables for a graph, it is an error to have an explicit error in the independent variable but not the dependent one. Thus you cannot graph temp with error zero versus voltage with error errVoltage.

If you are typing directly in the blank fields to define one of the variables for the graph, you may type in any valid Mathematica expression involving the variables. For example, if you wanted the error in the independent variable to be 10% of the value of temp, you could type directly in the final field, ending up with:

An introduction to simple Mathematica commands and syntax may be found here.

Making the Graph

The final section of the Setup screen looks like this:

The meanings of the buttons should be fairly self-evident.

• Make the graph: actually does the graph.
• Refresh: if you have entered a long and complex expression for one of the variables of the graph, it can easily be too long for the whole expression to be visible in the text box describing it. Clicking on this button will cause the size of the box to expand so that the entire expression is visible. It will also cause a button for that expression to appear in the array of buttons for the corresponding variable.
• Clear: clears this entire screen so you may start over. The screen will appear just as it did when it was first presented to you, before you clicked any buttons or typed into any fields.
• Options: provides access to various options to the grapher. Further information on these options may be found here.
• Terse: offers the same Setup screen functionality in a less verbose manner.
• End: ends the graph interface. This can be useful if you get things very messed up and/or wish to use changed or new data files.
• Help: provides access to this help message.

If you have already performed a graph with this session of the program, you will have the option or returning to this Setup screen to perform another graph. In this case the screen will have one and possibly two differences from as shown above:

1. The buttons on the bottom of the screen will include a Results button, which will return you to the Results screen for the previous graph.
2. If you have typed an expression to be used as a variable or error in the graph directly into the corresponding field, a button will now appear corresponding to that expression.

Click here to go to the top of this page.

The Results Screen

When you make a graph, the results are summarised by a single screen which presents both numerical and graphical information about the results of the fit, plus a section for deciding what to do next.

Imagine you have graph a dataset of voltage with error errVoltage versus temp with no explicit error to a straight line. The Results screen could look like this:

**** Graph number 1 **** voltage with error errVoltage versus temp with no error

What would you like to do now? Print these results Continue with another graph Go to terse mode Exit the graph program Help

Every Results screen has the same choices along the bottom. These are:

• Print these results. The Fit Results screen has been designed for presentation on a typical computer monitor. Choosing this option will display the same information in a form more suitable for printing.
• Continue with another graph. This takes you to the Setup screen for another graph.
• Go to terse mode. Display the same information without quite so many explanatory words. After being selected, the label on this button becomes Verbose.
• Exit the graph program. This can be useful if you get things very messed up and/or wish to use new data files.

Finally, the program stores every graph that you have done in a particular session. Imagine that you have chosen to do a second of the data, this time with no errors for either coorindate. Then the very bottom of the Result screen will look like this:

Thus you may toggle back and forth between the two (or more) graphs that you have made.

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Authors

This help document is Copyright © 1999, 2000 David M. Harrison. The sample screens are Copyright © 1999, 2000 Solomon R.C. Douglas and David M. Harrison. This is version 1.1 of the help document, date (m/d/y) 03/19/00.