how to plot with line ?

I have some selected point which I would like to show with line for example I import my data as follows:

load spectra
wl=[ 900:2:1700];
t1=[181 185 226 308 325] % First set of selected points
t2= [204 207 209 222 240 260 277 303]

then I try to plot them.

plot (wl, NIR)
hold on
ylim([-0.6 1.5])
plot (wl(1,t1),-0.2,'.b')
plot (wl(1,t2),-0.4 ,'.r')

But I want to plot it as follows:

Does anyone know how to do it? how to add those lines (not manually ?)

Answer 1

[dpb]

y1=[wl.NIR(3,t1); -0.2*ones(size(t1))]; % and y 

??? Attempt to reference field of non-structure

Why did you put the 'w1' in front of NIR()? You loaded NIR directly as we already had established; you've got to use the variables that are in your workspace, not mine.

y1=[NIR(3,t1); -0.2*ones(size(t1))];

[Niki]

I accept but you need to change something , however I managed to plot it; Thanks dear

[dpb]

Show your code where you had a problem--worked just fine here.

OK, I guess your 'w1' is actually 'wl' (a lowercase 'L' instead of a 'one') that I guessed when I did the edit.

Answer 2

[dpb]

OK, starting over -- I looked at your plot and see you really didn't use arrows at all--that makes it much simpler. Why TMW can't have an arrow that works much more easily is beyond me, but...

Start off as did before...presume you've already done the plot and ylim stuff--

hold on                                  % hold the plot to add onto it..  
x1=[w1(t1); w1(t1)];                     % the first set of x points
y1=[NIR(3,t1); -0.2*ones(size(t1))];     % and y
line(x1,y1,'color','b')                  % the vertical lines
scatter(x1(2,:),y1(2,:),'filled','facecolor','b','marker','d')  % and the markers at the ends

Now just repeat for the other set...

x2=[w1(t2); w1(t2)];
y2=[NIR(3,t2); -0.4*ones(size(t2))];
line(x2,y2,'color','r')
scatter(x2(2,:),y2(2,:),'filled','facecolor','r','marker','d')

So, if you're happy w/ this appearance, you can forget about the annotation stuff. I was trying to make it an arrow pointing down as thought at first glance that's what you'd drawn in your sample.

[Niki]

Thanks but still does not work. There are some functions you did not introduce before, what is f ? what is dat ? Matlab cannot recognise any of them

[dpb]

f was the frequency vector, 'dat' the structure name for the data...use your names in place; I guess you used w1 and didn't create a structure so it's NIR Figured that would be obvious.

[Niki]

I don't have frequency vector. I have frequency matrix named NIR x1=[NIR(t1); NIR(t1)];

when i use

hold on % hold the plot to add onto it.. x1=[NIR(t1); NIR(t1)]; % the first set of x points y1=[wl.NIR(3,t1); -0.2*ones(size(t1))]; % and y line(x1,y1,'color','b') % the vertical lines scatter(x1(2,:),y1(2,:),'filled','facecolor','b','marker','d') ??? Attempt to reference field of non-structure array.

I will get error