Question

matlb中没有cwt这类的小波变换函数怎么办？PS：利用 help cwt，就直接显示cwt not found.

Answer 1

有啊，help cwt
CWT Real or Complex Continuous 1-D wavelet coefficients.
COEFS = CWT(S,SCALES,'wname') computes the continuous
wavelet coefficients of the vector S at real, positive
SCALES, using wavelet whose name is 'wname'.
The signal S is real, the wavelet can be real or complex.

COEFS = CWT(S,SCALES,'wname','plot') computes
and, in addition, plots the continuous wavelet
transform coefficients.

COEFS = CWT(S,SCALES,'wname',PLOTMODE) computes and,
plots the continuous wavelet transform coefficients.
Coefficients are colored using PLOTMODE.
PLOTMODE = 'lvl' (By scale) or
PLOTMODE = 'glb' (All scales) or
PLOTMODE = 'abslvl' or 'lvlabs' (Absolute value and By scale) or
PLOTMODE = 'absglb' or 'glbabs' (Absolute value and All scales)

CWT(...,'plot') is equivalent to CWT(...,'absglb')

You get 3-D plots (surfaces) using the same keywords listed
above for the PLOTMODE parameter, preceded by '3D'. For example:
COEFS = CWT(...,'3Dplot') or COEFS = CWT(...,'3Dlvl').

COEFS = CWT(S,SCALES,'wname',PLOTMODE,XLIM) computes, and
plots, the continuous wavelet transform coefficients.
Coefficients are colored using PLOTMODE and XLIM.
XLIM = [x1 x2] with 1 <= x1 < x2 <= length(S).

For each given scale a within the vector SCALES, the
wavelet coefficients C(a,b) are computed for b = 1 to
ls = length(S), and are stored in COEFS(i,:)
if a = SCALES(i).
Output argument COEFS is a la-by-ls matrix where la
is the length of SCALES. COEFS is a real or complex matrix
depending on the wavelet type.

Examples of valid uses are:
t = linspace(-1,1,512);
s = 1-abs(t);
c = cwt(s,1:32,'cgau4');
c = cwt(s,[64 32 16:-2:2],'morl');
c = cwt(s,[3 18 12.9 7 1.5],'db2');
c = cwt(s,1:32,'sym2','lvl');
c = cwt(s,1:64,'sym4','abslvl',[100 400]);

See also wavedec, wavefun, waveinfo, wcodemat.
Reference page in Help browser
doc cwt

你可以在help中打开matlab help再打开search选项卡输入“cwt”。如果没有那就是你的matlab安装不完全，省略了帮助文档的安装，这在某些硬盘版的matlab安装包中很常见，一定要用光盘安装才行。
另外没有帮助文档但“cwt”这个函数可能还是可以用的，你可以敲个例子进去试试，或在tool boxes中看看有没有wavelet工具箱。

追问

我从toolbox 中查了一下没有 wavelet toolbox，请问是得重新下一个MATLAB么？

追答

如果toolboxes的more中最后没有wavelet，那就得重新装一个matlab，最好用光盘装。