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

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Yunus Mercan on 12 Apr 2021
Commented: Image Analyst on 12 Apr 2021
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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### Accepted Answer

Stephen23 on 12 Apr 2021
Edited: Stephen23 on 12 Apr 2021
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):
if t==1
2
3
4
5;
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:
Note that whilst it is certainly possible to plot vertical lines, your approach will not do this.
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Image Analyst on 12 Apr 2021
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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### More Answers (2)

Atsushi Ueno on 12 Apr 2021
1. 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.
2. 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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Yunus Mercan on 12 Apr 2021
Atsushi Ueno,It works fine this time, thank you for your interest.

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Jithin Nambiar J on 12 Apr 2021
Edited: Jithin Nambiar J on 12 Apr 2021
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');
Unless you plan to plot another graph in the same above plot. You don't need to use
hold on
Hope this helps. Cheers!
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Yunus Mercan on 12 Apr 2021
Thank you Jithin Nambiar J,It works fine.

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