Why is a straight line being plotted at zero, in addition to my desired plot?

I'm plotting distance (X) versus different in duration of a sound signal across two different conditions (Y).

When I plot just the raw differences, I can plot several comparisons, plus a dotted black line at Y=0 for a reference (neg vs. pos differences).

When I try to plot those differences as percents (basically, (Y2-Y1)/Y1), I get a solid color line at Y=0, in addition to the black dotted one. If I plot one line at a time I can see that this straight colored line comes up even when I'm just plotting one of them.

Please see attached figure for comparison/illustration.

Parts of the respective codes (they are largely identical):

Raw differences

%Taking differences from Baseline
OneD10DegDiff=OneD10Deg-OneDBaseline;
OneD20DegDiff=OneD20Deg-OneDBaseline;
OneD30DegDiff=OneD30Deg-OneDBaseline;
OneD40DegDiff=OneD40Deg-OneDBaseline;

TwoD10DegDiff=TwoD10Deg-TwoDBaseline;
TwoD20DegDiff=TwoD20Deg-TwoDBaseline;
TwoD30DegDiff=TwoD30Deg-TwoDBaseline;
TwoD40DegDiff=TwoD40Deg-TwoDBaseline;

%Plot
hold on
plot(Data1D(:,1),OneD10DegDiff,'-r','LineWidth',2);
plot(Data1D(:,1),OneD20DegDiff,'-m','LineWidth',2);
plot(Data1D(:,1),OneD30DegDiff,'-g','LineWidth',2);
plot(Data1D(:,1),OneD40DegDiff,'-b','LineWidth',2);

plot(Data2D(:,1),TwoD10DegDiff,'-.r','LineWidth',2);
plot(Data2D(:,1),TwoD20DegDiff,'-.m','LineWidth',2);
plot(Data2D(:,1),TwoD30DegDiff,'-.g','LineWidth',2);
plot(Data2D(:,1),TwoD40DegDiff,'-.b','LineWidth',2);

plot([0,180],[0,0],':k','LineWidth',2);
axis([0 180 -0.25 0.1])
title([Name ' Percent Difference from Baseline'])
xlabel('Target Distance')
ylabel('Percent Duration Difference from Baseline (in ms)')

For percent differences:

%Taking differences from Baseline
OneD10DegDiff=(OneD10Deg-OneDBaseline)/OneDBaseline;
OneD20DegDiff=(OneD20Deg-OneDBaseline)/OneDBaseline;
OneD30DegDiff=(OneD30Deg-OneDBaseline)/OneDBaseline;
OneD40DegDiff=(OneD40Deg-OneDBaseline)/OneDBaseline;

TwoD10DegDiff=(TwoD10Deg-TwoDBaseline)/TwoDBaseline;
TwoD20DegDiff=(TwoD20Deg-TwoDBaseline)/TwoDBaseline;
TwoD30DegDiff=(TwoD30Deg-TwoDBaseline)/TwoDBaseline;
TwoD40DegDiff=(TwoD40Deg-TwoDBaseline)/TwoDBaseline;

%Plot
hold on
plot(Data1D(:,1),OneD10DegDiff,'-r','LineWidth',2);
plot(Data1D(:,1),OneD20DegDiff,'-m','LineWidth',2);
plot(Data1D(:,1),OneD30DegDiff,'-g','LineWidth',2);
plot(Data1D(:,1),OneD40DegDiff,'-b','LineWidth',2);

plot(Data2D(:,1),TwoD10DegDiff,'-.r','LineWidth',2);
plot(Data2D(:,1),TwoD20DegDiff,'-.m','LineWidth',2);
plot(Data2D(:,1),TwoD30DegDiff,'-.g','LineWidth',2);
plot(Data2D(:,1),TwoD40DegDiff,'-.b','LineWidth',2);

plot([0,180],[0,0],':k','LineWidth',2);
axis([0 180 -0.25 0.1])
title([Name ' Percent Difference from Baseline'])
xlabel('Target Distance')
ylabel('Percent Duration Difference from Baseline (in ms)')

[Varun Lal]

Please help me out with this too.

t=data(:,1);

Ax=data(:,2);

Ay=data(:,3);

Az=data(:,4);

r=(Ax.^2 + Ay.^2 + Az.^2).^(1./2);

plot(t,Ax)

this is a plot of accleration vs time.

Answer 1

[Star Strider]

I don’t have your data and you didn’t describe it (I assume all are vectors), so see if doing the element-wise division makes a difference:

OneD10DegDiff=(OneD10Deg-OneDBaseline)./OneDBaseline;

Note the (./) in place of (/).

[B.M.]

I knew it had to be something ridiculously simple like that. Haven't used those since I worked through an intro book a while ago. Thanks!

[Star Strider]

My pleasure!

Answer 2

[Andrew Reibold]

You have the following line

plot([0,180],[0,0],':k','LineWidth',2);

This plots a line from 0 to 180, with values from 0 to 0. So it will leave a straight line at zero. If you didn't write that, it may just be a baseline for people to see where zero is :-)

If you remove it, does it still show up?

[B.M.]

This is the black dotted line (format :k), which I did put in as a reference. I don't get where the colored line is coming from (cycles through red, magenta, green, then blue, so looks blue in the graphic). If I just plot the red line,

plot(Data1D(:,1),OneD10DegDiff,'-r','LineWidth',2);

This is what I get. (see attachment)