How to plot function

Question

Hardik 2014-7-29

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评论： Ben11 2014-7-30

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I'm working on a question where I am executing a function y = staircase(x) where

y = [ 0 if x <= 1 , 1 for 1<x<=2 & 2 if 2<x ]

So far I have;

function y = staircase(x)
for x = -3:0.01:3
  if x <= 1
      y = 0;
  elseif x > 1 && x <= 2
      y = 1;
  else x > 2;
      y = 2;
  end
end

My question is how do I plot such a function?

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Answer 1

Ben11 2014-7-29

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A lazy way would be like this:

figure
hold on
plot((-3:0.01:1),0,(1.01:0.01:2),1,(2.01:0.01:3),2,'LineWidth',2)
line('XData',[1 1],'YData',[0 1],'LineStyle',':');
line('XData',[2 2],'YData',[1 2],'LineStyle',':');
hold off

which gives this:

Do you need to write the plotting part in your function or you simply want to look at the staircase for some other purpose?

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Answer 2

Azzi Abdelmalek 2014-7-29

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编辑：Azzi Abdelmalek 2014-7-29

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x is an input argument, you can't assign values to x inside the function.

save this function as staircase.m

function y = staircase(x)
for k=1:numel(x)
  if x (k)<= 1
    y(k) = 0;
  elseif x(k) > 1 && x(k) <= 2
    y(k) = 1;
  else x(k) > 2
    y(k)= 2;
  end
end

Then in Matlab Windows Command or in a new script write

x=-3:0.1:3 ; %assign values to x
y = staircase(x);
plot(x,y)

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Hardik 2014-7-30

When I run the script with the addition of the numel, matlab gives me an error saying Not enough input arguments.

Ben11 2014-7-30

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As Azzi suggested, you have to define x before you call staircase. I ran his code and it works well. Do the following:

1) Define x in the command window

x = -3:0.1:3;

2) Once this is done, you can then call staircase(x) and plot the result:

y = staircase(x);
plot(x,y)

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Answer 3

Star Strider 2014-7-29

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I built my own staircase function, because I didn’t want to create a separate function file.

This is how I plotted it:

x = -3:0.01:3;
staircase = @(x) [(0*(x <= 1)) + (1*((x > 1) & (x <= 2))) + (2*(x > 2))];
sc = staircase(x);
figure(1)
plot(x, sc)
axis([xlim    -0.5  2.5])