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

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.

[the cyclist]

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

Can you post the full code that gives that warning?

[Walter Roberson]

Simple testing does not appear to show that message?

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

Answer 1

[Norman]

Here is the code that gives the warning

X = compassplot(ones)

[Paul]

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]

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]

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.

●