# Documentation

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# mexihat

Mexican hat (Ricker) wavelet

## Syntax

`[PSI,X] = mexihat(LB,UB,N)`

## Description

`[PSI,X] = mexihat(LB,UB,N)` returns values of the Mexican hat wavelet on an `N` point regular grid, `X`, in the interval `[LB,UB]`. The Mexican hat wavelet is also known as the Ricker wavelet.

Output arguments are the wavelet function `PSI` computed on the grid `X`.

This wavelet has [-5 5] as effective support. Although [-5 5] is the correct theoretical effective support, a wider effective support, [-8 8], is used in the computation to provide more accurate results.

This function is proportional to the second derivative function of the Gaussian probability density function.

 Note:   You can use `gauswavf` to obtain a second order derivative of a Gaussian wavelet. If you use the negative of this normalized derivative, the resulting wavelet resembles the Mexican hat wavelet.

## Examples

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Create a Mexican hat wavelet with support on [-5,5]. Use 1,000 sample points. Plot the result.

```lb = -5; ub = 5; N = 1000; [psi,xval] = mexihat(lb,ub,N); plot(xval,psi) title('Mexican Hat Wavelet'); ```