My plot comes up as a white graph with no line.

Question

Yunus Mercan 2021-4-12

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评论： Image Analyst 2021-4-12

When I try to plot with this code which is given below, nothing comes up. There are no errors, there's just a blank page. I want to lines between y values depending t values.

Please help me. Thank you from now.

clear all;
clc;
  for t=1:25
        
        if t==1,2,3,4,5;
            y(t) = 1
            
        elseif t==6,7,8,9,10;
                    y(t) = 0.9
        
            elseif t==11,12,13,14,15,;
                         y(t) = 1
                         
                elseif t==16,17,18,19,20,;
                         y(t) = 1.05
                    
                      elseif t==21,22,23,24,25,;
                         y(t) = 1
           
            end
  end
figure
hold on;plot(t, y)
xlabel('t(1/100)'); ylabel('VR'); 
title('VR Değişimi');

Expected graph is like that

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Answer 1

Stephen23 2021-4-12

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编辑：Stephen23 2021-4-12

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The basic problem is that this syntax

if t==1,2,3,4,5;

is equivalent to writing this (i.e. each expression is evaluated independently):

That is not the correct way to compare mulitple values at once. Remember that the name MATLAB comes from MATrix LABoratory: you should always keep your data in vectors/matrices/arrays. For example:

if any(t==[1,2,3,4,5])
%         ^^^^^^^^^^^ vector!

Note that you should preallocate y before the loop:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

Note that whilst it is certainly possible to plot vertical lines, your approach will not do this.

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Yunus Mercan 2021-4-12

Thank you Stephen Cobeldick , it worked.

Image Analyst 2021-4-12

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Instead of an if/else, a switch statement can be used to compare multiple cases at a time. For example:

switch(result)
   case 1
      disp('result is 1')
   case {52, 78}
      disp('result is 52 or 78')
end

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Answer 2

Atsushi Ueno 2021-4-12

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After exexuting your script, y is like [1 0 0 0 0 0.9 0 0 0 0 1 ....] it must be different from what you expected.
After executinf for loop, the variable t is going to be deleted. So, you need t = 1:25 after the for loop.

How about the code below?

clear all;
clc;
t = 1:25;
y = repelem([1 0.9 1 1.05 1], 1, 5);
figure
hold on;
plot(t, y)
xlabel('t(1/100)');
ylabel('VR'); 
title('VR Değişimi');

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Atsushi Ueno 2021-4-12

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How about using stem(t, y) or stairs(t, y) instead of plot(t, y)?

You have to care about index for using other functions.

clear all;
clc;
t = 0:24; % just changed from 1:25 for stairs()
y = repelem([1 0.9 1 1.05 1], 1, 5);
figure
hold on;
stairs(t, y);
xlabel('t(1/100)');
ylabel('VR'); 
title('VR Değişimi');

Yunus Mercan 2021-4-12

Atsushi Ueno,It works fine this time, thank you for your interest.

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Answer 3

Jithin Nambiar J 2021-4-12

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编辑：Jithin Nambiar J 2021-4-12

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Your code can get pretty long and tedious. The if statement in your code would not work well because it wont compare the values separated by commas properly.

t=0.0001:0.01:40;
x=[t>0]-0.05.*[t>5]+0.05.*[t>15]+0.05.*[t>25]-0.05.*[t>35];
plot(t,x)
grid on;
xlabel('t(1/100)'); ylabel('VR'); 
title('VR Değişimi');