straight line doesn't show in plot

Horizontal line doesn't appear in the plot for some reason. if I add 'x' or different line marker in the plot command it appears in the plot.

Scipt:

%%Stress distribution in the thick-walled and thin-walled cylinder along the cylinder wall
%%Constants and radial distance through the wall
Pi=13.1; % N/mm^2 internal pressure
d0=68; % mm outer radius
N=100; % number of points through the wall
t=6; % mm wall thickness
a=(d0-2*t)/2; % mm internal radius
b=d0/2; % mm external radius
k=b./a; % constant
r=linspace(a,a+t,N); % mm radial distance from the centre
p=(r-a)/t; % parametric distance
%%thin-walled cylinder
thinsigma1=Pi*a./t; % 1st principal stress
thinsigma2=Pi*a./(2*t); % 2nd principal stress
thinsigma3=0; % 3rd principal stress
%%thick-walled cylinder
thicksigma1=(Pi/((k^2)-1))*(1+(b^2)./(r.^2)); % 1st principal stress
thicksigma2=Pi/((k^2)-1); % 2nd principal stress
thicksigma3=(Pi/((k^2)-1))*(1-(b^2)./(r.^2)); % 3rd principal stress
%%plot the results for thin-walled cylinder
plot(p,thinsigma1,'kx')
title('Thin-walled principal stress versus parametric distance')
legend('1st principal stress')
xlabel('Parametric distance')
ylabel('1st principal stress, N/mm^2')
figure()
plot(p,thinsigma2,'kx')
title('Thin-walled principal stress versus parametric distance')
legend('2nd principal stress')
xlabel('Parametric distance')
ylabel('2nd principal stress, N/mm^2')
figure()
plot(p,thinsigma3,'kx')
title('Thin-walled principal stress versus parametric distance')
legend('3rd principal stress')
xlabel('Parametric distance')
ylabel('3rd principal stress, N/mm^2')
%%plot results for thick-walled cylinder
figure()
plot(p,thicksigma1)
title('Thick-walled principal stress versus parametric distance')
legend('1st principal stress')
xlabel('Parametric distance')
ylabel('1st principal stress, N/mm^2')
figure()
plot(p,thicksigma2)
title('Thick-walled principal stress versus parametric distance')
legend('2nd principal stress')
xlabel('Parametric distance')
ylabel('2nd principal stress, N/mm^2')
figure()
plot(p,thicksigma3)
title('Thick-walled principal stress versus parametric distance')
legend('3rd principal stress')
xlabel('Parametric distance')
ylabel('3rd principal stress, N/mm^2')

line doesn't appear in the first 3 figures (in this script I put 'kx' so it appears) and in figure 5.

anyone knows why it is so?

Answer 1

[dpb]

Second posting today with same issue...serendipity strikes again!!! :)

>> whos p thinsig*
Name            Size             Bytes  Class     Attributes

p               1x100              800  double              
thinsigma1      1x1                  8  double              
thinsigma2      1x1                  8  double              
thinsigma3      1x1                  8  double              
>>

All the y values are single points--when given a vector of x values but a single y, plot draws a line for each x value consisting of the single point. Hence, you get a dotted line by default or the markers when using the 'x' marker type.

If it really is intended to be a horizontal line, no point in filling a full array, but do have to fix up the plotting command somehow...

plot(p,repmat(thinsigma1,size(p)),'k')

is effective but a hammer.

plot(p([1 end]),repmat(thinsigma1,1,2),'k')

is more efficient in memory.

[Povilas Vaitukaitis]

thank you!

[dpb]

No problem...was, however, curious event of two unrelated cases of the same symptom showed up on same day and I don't recall it ever in the time since I started watching the forum...

BTW, if have Stat and Machine Learning TB, there's a prepackaged function refline to add a baseline included there that's some "syntactic sugar" to accomplish the deed. Seems like a useful additive method to the plot function instead of squirreling away in a toolbox, however. But, of course, it's a pretty trivial addition.