Matlab 的table數據使用

Matlab可用來大量讀數據的function

https://www.mathworks.com/help/matlab/datastore.html

readtable的使用

讀入數據

t = readtable(filename)

讀入特定範圍數據

T = readtable('filename.xls', 'Range', 'C2:E6', 'ReadVariableNames', false)

觀看table特性

t.Properties

呼叫數據，使用圓括號()，返回值為table，若使用{}則返回cell

t(2, :)

直接使用變數名稱會回傳該Row值，如：t.Variable1

Matlab批次處理excel

最近一直在用matlab，順手紀錄一下，方便未來查閱

批次讀取檔案路徑，好用的函數dir

讀寫excel的函數xlsread、xlswrite

範例

path = 'YourFolderPath';

% return all of files of the folder

Files = dir(strcat(path,'*.xlsx'));

LengthFiles = length(Files);

for i = 1:LengthFiles

%批次讀取檔案

[number, text, rawData] = xlsread(strcat(path,Files(i).name));

end

參考資料：

1. https://www.mathworks.com/help/matlab/ref/dir.html
2. https://www.mathworks.com/help/matlab/ref/xlswrite.html
3. https://www.mathworks.com/help/matlab/ref/xlsread.html

matlab濾波器設計

1. 選定濾波器與其規格，以下隨意兩項會決定另一項的數值
• Filter order
• Transition width
• Peak passband/stopband ripple
2. 使用fvtool function檢查濾波器圖形
3. 檢查Group delay
4. shift訊號或是選用zero-phase filter來消除Group delay

FIR vs IIR

• IIR相比FIR有較少的濾波器階數，資源消耗較少
• IIR的group delay是非線性的

範例：

%Bandpass filter with Passband [50 400], Stopband frequency [45 405], Stopband attenuation [60], Passband Ripple [1000]. 

BPfilt = designfilt('bandpassfir', 'StopbandFrequency1', 45, 'PassbandFrequency1', 50, 'PassbandFrequency2', 400, 'StopbandFrequency2', 405, 'StopbandAttenuation1', 60, 'PassbandRipple', 1, 'StopbandAttenuation2', 60, 'SampleRate', 1000);

fvtool(BPfilt) %檢查濾波器波型

grpdelay(BPfilt) %檢查Group delay

D = mean(grpdelay(BPfilt));% Shift data去補償Group delay的影響 

y = filter(BPfilt,[YourData; zeros(D,1)]);  % 增加D zeros

y = y(D+1:end); 

相關文章：

• https://www.mathworks.com/help/signal/ref/designfilt.html
• https://www.mathworks.com/help/signal/ug/practical-introduction-to-digital-filter-design.html
• https://www.mathworks.com/help/signal/ug/practical-introduction-to-digital-filtering.html
• https://www.mathworks.com/help/signal/ref/filtfilt.html