# Plotting a spiral with SigmaPlot

• maverik
In summary, the conversation discusses the use of the 'Regression Wizard' in SigmaPlot to obtain a best-fit curve for a data set of 15 points that map out a logarithmic spiral. The individual is struggling to find the correct equation category and is unsure how to set a user-defined equation. They also provide possible equations in polar and cartesian coordinates and express interest in any advice or resources on plotting spirals.

#### maverik

I am trying to use the 'Regression Wizard' in SigmaPlot to obtain a best-fit curve to a data set of ~15 data points that map out a spiral. None of the equation categories given in the regression wizard seem to work (i.e. polynomial, exponential, logarithm, hyperbola etc. etc.) and I am unsure how to set a user defined equation to the data set.

It's a logarithmic spiral so I'm assuming the eqn in polar co-ords should be;

r(theta)=a*exp(b*theta)

parametrically it should be;

x=r*cos(theta)=a*cos(theta)*exp(b*theta)
y=r*sin(theta)=a*sin(theta)*exp(b*theta)

and in cartesian co-ords;

x^2+y^2=exp((theta)*cot(a))

Any advice on SigmaPlot or plotting spirals in general will be greatly appreciated!

Hi,
i hope this link might be useful
http://www1.webng.com/economics/logspiral.txt [Broken]

source Mishra

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## 1. How do I plot a spiral with SigmaPlot?

To plot a spiral with SigmaPlot, follow these steps:

• Go to the "Graph" menu and select "XY Graph".
• In the "Data" tab, click on the "Add" button and select "Curve".
• In the "Equation" tab, click on the "Add" button and select "Polar Equation".
• In the equation editor, enter the equation for a spiral, such as "r = a*theta", where "a" is a constant.
• Adjust the axis limits and other graph settings as desired, then click "OK" to plot the spiral.

## 2. Can I customize the appearance of the spiral in SigmaPlot?

Yes, you can customize the appearance of the spiral in SigmaPlot by changing the line style, color, and thickness in the "Curve" settings. You can also change the color and size of the markers, and add a legend if desired.

## 3. How can I plot multiple spirals on the same graph in SigmaPlot?

To plot multiple spirals on the same graph in SigmaPlot, follow these steps:

• Create a new "Curve" for each spiral, using the same method as for plotting a single spiral.
• Select all the curves by clicking on them while holding down the CTRL key.
• Right-click on one of the curves and select "Group".
• Adjust the axis limits and other graph settings as desired, then click "OK" to plot the multiple spirals.

## 4. Is it possible to add labels and annotations to a spiral plot in SigmaPlot?

Yes, you can add labels and annotations to a spiral plot in SigmaPlot by using the "Text" and "Arrow" tools in the "Tools" menu. You can also add a title and axis labels in the "Graph Properties" menu.

## 5. Can I export my spiral plot from SigmaPlot to another program?

Yes, you can export your spiral plot from SigmaPlot to another program by going to the "File" menu and selecting "Export". You can choose from various file formats, including image files (such as PNG or JPEG) or data files (such as CSV or TXT).