GraphPad Curve Fitting Guide

Sinc wave

Sinc wave

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Sinc wave

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Introduction

The sinc() function appears frequently in signal and image processing because it is the Fourier transform of a rectangular pulse. It is also called the "sampling" or "sine cardinal" function.

Step by step

Create an XY data table. There is one X column, and many Y columns. If you have several experimental conditions, place the first into column A, the second into column B, etc.

After entering data, click Analyze, choose nonlinear regression, choose the panel of equations for sine waves, and choose Sinc() function.

You may need to fuss with the initial values for Phaseshift and Wavelength, as our built-in rules for computing the initial value doesn't always work very well.

Model

Y=IF(X=0,Amplitude,Amplitude*sin(2*pi*X/Wavelength)/(2*pi*X/Wavelength) )

Interpret the parameters

Amplitude is the height of top of the waves, in Y units.

Wavelength is the time it takes for a complete cycle, in units of X

Frequency is the number of cycles per time unit. It is calculated as the reciprocal of wavelength, and is expressed in the inverse of the time units of X.