Unwrap does not work for vector

Question

Will Hardiman 2022-1-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1635175-unwrap-does-not-work-for-vector

回答： Will Hardiman 2022-1-24

I have a vector, y, calculated as atan(a/b). Naturally when b is close to 0 the tan function exhibits a phase wrap:

y = atan(a/b);
plot(y)
title('Wrapped function')

I can manually check the jump size:

plot(diff(y))
title('Y(n) - Y(n-1)')

Clearly there are jumps greater than 3. But when I use unwrap:

plot(unwrap(y,3))
title('"Unwrapped" function')

The function clearly is not unwrapped. Note I have used a tolerance of 3, and there are differences larger than 3. Even if I set the tolerance to 0.1, the same behaviour occurs.

I have tested this on R2019a and R2020a and see the same behaviour.

What have I done wrong?

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Answer 1

Will Hardiman 2022-1-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1635175-unwrap-does-not-work-for-vector#answer_880825

在 MATLAB Online 中打开

I just re-read the documentation for unwrap, where it clearly says:

Q = unwrap(P,tol) compares the jump between elements of P to the jump threshold tol instead of the default value π radians. If you specify a jump threshold less than π, unwrap uses the default jump threshold π.

Perhaps unwrap should give a warning when tol < pi, because it's misleading otherwise?