[beginner] How do you plot two vectors of diffrent length?

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Emanuel Strid 2021-9-7

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回答： Steven Lord 2021-9-8

Hi,

How do you go about to plot two vectors of diffent lengths in Matlab? One of my homework assignments is to great a plot graph using these two vectors:

x1 = [1 2 3 4 5 6]

y1 = [3,5 4,8 7,1 9,1 10,5 13,2]

However, this seems impossible due to the nature of the plot function, where it demands vectors to be of same length. I tried plot(x1, y1) and that didn't work. We haven't gotten anymore information than this :(

Maybe the teacher inserted a comma when it should've been a decimal point inside vector y1? He's Swedish, so maybe that's why.

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Answer 1

Dave B 2021-9-7

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编辑：Dave B 2021-9-7

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At some level the question is what you expect from the plot.

When I look at your y1 vector, I notice that it's got an odd arrangement of commas and spaces. I wondered if maybe it was intending to make a 2x6 or 6x2 matrix, which would make a lot of sense to plot against the numbers 1 to 6.

x1 = [1 2 3 4 5 6];

y1 = [3 5;4 8;7 1;9 1;10 5;13 2];

plot(x1,y1)

More generally, to answer the title, you can plot two different length vectors as follows:

y1 = rand(1,5);

y2 = randn(1,7);

plot(y1)

hold on

plot(y2)

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Emanuel Strid 2021-9-7

编辑：Emanuel Strid 2021-9-7

Thank you so much! A matrix makes much more sense! I guess my teacher incorrectly arranged the y1 vector with commas. I was just perplexed as he had never mentioned a syntax like that

Dave B 2021-9-7

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Happy to help, sometimes writing code involves a certain amount of mind-reading.

But just to be clear, the semicolons are the really critical bit, commas and spaces are the same when specifying a matrix (but I like the way it looks without the commas:

y1 = [3 5;4 8;7 1;9 1;10 5;13 2]; 
y2 = [3,5;4,8;7,1;9,1;10,5;13,2]; 
isequal(y1,y2)
ans = logical
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Answer 2

Steven Lord 2021-9-8

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I believe your suspicion about whether the commas should be periods is correct. MATLAB uses the convention that the decimal separator is the period, but another convention is to use a comma.

x1 = [1 2 3 4 5 6];

y1 = [3.5 4.8 7.1 9.1 10.5 13.2];

plot(x1, y1)