Unwrap lower than the default value (pi)

Question

Pranjal Agrawal 2023-8-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2005722-unwrap-lower-than-the-default-value-pi

评论： Bryan Wingert 2024-7-16，20:49

Hi! Can anyone please elaborate on how to eliminate jumps that are less than pi?I have a function which varies from (0,pi/2). I want to unwrap the values in between that range. Can anyone please suggest on how to use this.

Thanks

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Stephen23 2023-8-7

multiply by four, UNWRAP, divide by four

Bryan Wingert 2024-7-16，20:49

This is a pretty clever hack of the unwrap function. It scales jumps from the threshold (pi/2 in this case) up to 2*pi, which guarantees that it gets unwrapped, since the unwrap function looks for jumps of 2*pi. (The threshold represents the bidirectional bound, e.g. [-pi,pi] for the default.) More specifically, the scaling factor is approximately 2*pi/threshold. Approximately because numerical error can throw it off sometimes.

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Answer 1

Sanjana 2023-8-21

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https://ww2.mathworks.cn/matlabcentral/answers/2005722-unwrap-lower-than-the-default-value-pi#answer_1290292

在 MATLAB Online 中打开

Hi Pranjal,

I understand that you are looking for a way to eliminate jumps that are less than pi. As per the official documentation of the,”unwrap” function, if a jump threshold less than pi is specified, then unwrap function uses the default jump threshold pi.

For eliminating jumps that are less than pi, a custom unwrapping algorithm can be implemented as follows,

% Let P be the phase vector
%Intialize unwrapped phase vector 
unwrapped = zeros(size(P));
unwrapped (1) = P(1);
for i = 2:length(P)
    diff = P(i)-P(i-1);%Calculating the jump
    %check if jump is greater than threshold T
    if diff > T
        unwrapped(i) = P(i) - 2*pi;
    elseif diff < -T
        unwrapped(i) = P(i) + 2*pi;
    else
        unwrapped(i) = P(i);
    end
end

Please refer to this following link, for further information,

https://www.mathworks.com/help/matlab/ref/unwrap.html

Hope this helps!

Regards,

Sanjana

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Bryan Wingert 2024-7-16，20:31

This only unwraps the point next to the jump, and leaves the rest of the vector untouched. The unwrap function cumulatively shifts the rest of the vector. Use Stephen23's hack above.

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