Need to stop warning because i need to not show a plot using compassplot

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Norman 2025-12-8

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https://ww2.mathworks.cn/matlabcentral/answers/2181725-need-to-stop-warning-because-i-need-to-not-show-a-plot-using-compassplot

评论： Paul 2025-12-19

Warning: Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.

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the cyclist 2025-12-8

I don't recognize that as a warning from a MATLAB function.

Can you post the full code that gives that warning?

Walter Roberson 2025-12-9

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Simple testing does not appear to show that message?

compassplot([1 2+3i 2-3i])

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Answer 1

Norman 2025-12-19

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Here is the code that gives the warning

X = compassplot(ones)

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Paul 2025-12-19

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The function ones as called returns 1.

ones
ans = 1

Apparently, sending a real vector as the input generates that warning

figure;tiledlayout(1,2)

nexttile

X = compassplot(ones);

Warning: Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.

nexttile

X = compassplot([1,-1]);

Warning: Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.

●

To avoid the warnings, you can turn the warning off, plot, then turn back on.

[msgstring,warnid] = lastwarn % to see what the warning ID is

msgstring = 'Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.'

warnid = 'MATLAB:polar:AssumeComplex'

figure;tiledlayout(1,2);

nexttile

warnstruct = warning('off',warnid)

warnstruct = struct with fields:

identifier: 'MATLAB:polar:AssumeComplex' state: 'on'

X = compassplot(ones);

nexttile

X = compassplot([1,-1]);

warning(warnstruct); % return to previous state

Walter Roberson 2025-12-19

在 MATLAB Online 中打开

Oddly enough, if you do provide something with real and imaginary components, you do not get the warning.

compassplot(1)

Warning: Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.

●

compassplot(1+2i)

Paul 2025-12-19

在 MATLAB Online 中打开

I can only guess from the text of the warning that the developers assume that if the user inputs a value with a non-zero imaginary part that the user meant it, but if the input has zero imaginary part then the user might be making a mistake (not sure what that mistake could be). But I could be wrong because the behavior is documented, though one could argue it could be a tad more clear on this particular case. Personally, I think this warning is overkill, though I'd be interested if there's some corner case where it helps keep the user from doing something unintended.

Note that the warning still shows up even if the input explicitly has a complex attribute

x = complex(1,0);

whos x

Name Size Bytes Class Attributes x 1x1 16 double complex

compassplot(x)

Warning: Plotting the real and imaginary components of the value provided. Specify both R and Theta values if you do not intend to plot a complex value.

●

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Need to stop warning because i need to not show a plot using compassplot

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