先說一下字串，字串在matlab中需要加單引號，你直接使用newData1 = importdata(DOW.txt);

matlab便會將DOW.txt看成是變數，但是importdata需要一個包含檔名的字串變數，但是DOW.txt不知道是什麼東西，所以會出現??? Undefined variable "DOW" or class "DOW.txt".

正確的使用方法是：

newData1 = importdata("DOW.txt");

或者

path="DOW.txt"

newData1 = importdata(path);

不過importdata不支援字尾名為txt檔案，其支援的檔案字尾有：

Data formats Command Returns

MAT - MATLAB workspace load Variables in file.

CSV - Comma separated numbers csvread Double array.

DAT - Formatted text importdata Double array.

DLM - Delimited text dlmread Double array.

TAB - Tab separated text dlmread Double array.

Spreadsheet formats

XLS - Excel worksheet xlsread Double array and cell array.

WK1 - Lotus 123 worksheet wk1read Double array and cell array.

Scientific data formats

CDF - Common Data Format cdfread Cell array of CDF records

FITS - Flexible Image Transport System fitsread Primary or extension table data

HDF - Hierarchical Data Format hdfread HDF or HDF-EOS data set

Movie formats

AVI - Movie aviread MATLAB movie.

Image formats

TIFF - TIFF image imread Truecolor, grayscale or indexed image(s).

PNG - PNG image imread Truecolor, grayscale or indexed image.

HDF - HDF image imread Truecolor or indexed image(s).

BMP - BMP image imread Truecolor or indexed image.

JPEG - JPEG image imread Truecolor or grayscale image.

GIF - GIF image imread Indexed image.

PCX - PCX image imread Indexed image.

XWD - XWD image imread Indexed image.

CUR - Cursor image imread Indexed image.

ICO - Icon image imread Indexed image.

RAS - Sun raster image imread Truecolor or indexed.

PBM - PBM image imread Grayscale image.

PGM - PGM image imread Grayscale image.

PPM - PPM image imread Truecolor image.

Audio formats

AU - NeXT/Sun sound auread Sound data and sample rate.

SND - NeXT/Sun sound auread Sound data and sample rate.

WAV - Microsoft Wave sound wavread Sound data and sample rate.