A graph in matlab, needs some guidance

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googo 2013-3-26

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Hey,

First question : Suppose I have two vectors : x = [1 2 3] and y=[0.5,0.35,0.15] and I want to draw a graph using only the plot function but I'm intrested that from 1-2 y will be 0.5 ,from 2-3 y will be 0.35 and from 3+ y will be 0.15... like steps.

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How can I do it?

Second quesition: how do I combine xlim and ylim functions in the plot function?

thank's!

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Walter Roberson 2013-3-26

please review the guide to tags and retag your question. see http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

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Answer 1

Mike Garrity 2013-3-26

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在 MATLAB Online 中打开

The stair function is probably closer to what you want, but you can do it with plot if you tell it what to do in detail.

Basically, you need to add a new point for the end of each line segment, and another point "between" the line segments. That third point will get the value nan to tell the plot command to stop drawing. Here's a MATLAB-golf like solution:

x2=repmat(x,[3,1]);
y2=repmat(y,[3,1]);
x2(:,4)=numel(x);
y2(3,:)=nan;
plot(x2(3:11),y2(:))

What's going on is that the two calls to repmat give us 3 copies of the X and Y values. Now we add the value 4 onto the end of the X values to get the right side of the last line. And we stick nans into the last row of the Y values.

Finally when we plot them, we need the X and Y values to be out of phase. This makes the X change between the first two points, then the Y change between the next pair, etc.

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Answer 2

Wayne King 2013-3-26

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编辑：Wayne King 2013-3-26

在 MATLAB Online 中打开

   x = 1:0.1:4-0.1;
   y = [0.5 0.35 0.15];
   ynew = zeros(size(x));
   ynew(1:10:end) = y;
   ynew = filter(ones(10,1),1,ynew);
   stem(x,ynew);
   set(gca,'xlim',[1 3.5]);
   set(gca,'ylim',[0 0.6]);
   grid on;

If you use

plot(x,ynew)

above you'll get a sloped line where your plot actually has a discontinuity, so if you don't like stem(), use

   stairs(x,ynew)
   set(gca,'xlim',[1 3.5]);
   set(gca,'ylim',[0 0.6]);
   grid on;

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Answer 3

googo 2013-3-26

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thank's for the comments! but isn't there any simpler code? it's one of my first exercises in matlab and I don't think we are alowed using those functions... thank's any way...

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Image Analyst 2013-3-26

Stairs() is a legitimate function of MATLAB. That is the simplest way. The 3 other lines Wayne added are just to make the graph pretty. By the way, your "Answer" here should have been a comment to Wayne's answer, not an "Answer" in itself. If you can't use certain functions then please list which functions are banned, and if possible say why those certain functions are banned while other are okay. Is there any rationale to it?

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