Sematics of freqz in Help

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Max Yaffe 2023-4-13

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评论： Gokul Nath S J 2023-4-24

Looking at freqz in the help system there are several ways to invoke the function:

[h,w] = freqz(b,a,n) % 2 real coefficients vectors, and # of points

[h,w] = freqz(sos,n) % 1 sections-matrix, and # of points

[h,w] = freqz(d,n) % 1 matrix containing row of b's and row of a's, and # of points

[h,w] = freqz(___,n,'whole') % any of the above with n points around unit circle from 0 to 2pi

[h,f] = freqz(___,n,fs) % as above but frequencies normalized to fs

[h,f] = freqz(___,n,'whole',fs) % and so forth

h = freqz(___,w)

h = freqz(___,f,fs)

freqz(___)

What is the meaning of the '___'?

My best guess is that Matlab implies the signature of the function based on the data types of the arguments, and that '___' could be either 'b,a' or 'sos' or 'd'

Is this correct? Are there any other string parameters that freqz could take?

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Paul 2023-4-13

Hi Max,

I too am often confused by this. Too bad there's not a doc page in the doc that explains how to interpret the syntax section of doc page of a function. At least I've not been able to find it.

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Answer 1

Gokul Nath S J 2023-4-20

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编辑：Gokul Nath S J 2023-4-20

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Hi Max,

Based on your question, it seems that you would like to know the meanig of '___'. Basically the notation '___' is used when documentation is emphasising on the arguments coming after '___', so that there won't be much confusion on which part of the argument the document is refering to.

For an example, if the following code is considered, the document is giving emphasis on the argument w itself.

h = freqz(___, w)

By using such a notation, there won't be any confusion on which part of the function, the document is refering to. Further, as you suggested '___', can imply any other argument which is currently out of relevance while mentioning a particular argument field

Thanks,

Gokul Nath S J

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Max Yaffe 2023-4-23

Thanks for the answers Gokul, but the semantics are not consistent and open to interpretation.

For example in "[h,w] = freqz(___,n,'whole')" could mean b,a or sos, or d, with the callee implying which using argument type.

By argument type, I also imply if a string like 'whole' is found (anywhere?), it is interpreted as an ad hoc control parameter.

But what does '____' mean in h = freqz(___,w)? Does it include the 'n'? does it include 'fs'?

Gokul Nath S J 2023-4-24

Hi Max,

It is true that, once it depicts '____', the users are not sure which input arguments does it mean as you have mentioned as it could be b, a or sos or d. However, the purpose of [h, w] = freqz(___, w) can include n as well as fs but the main concern is defining the parameter w.

Thanks

Gokul Nath S J

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