# I have doubts about using Pots.jl

I’m trying to plot this function x = 0.2 * cos (2 * t + π) but there is something wrong with the definition of t.

"

using Pkg
using Plots

t=range(0,stop=10, length=100) #0:0.01:2π
y = 0.2
cos.(2*t+π)

plot(t, y, label=“cos(x)”)
plot!(xlab=“t(s)”, ylab=“x(m)”)

"

Yeah, it’s a typo. lenght is spelled length.

You also don’t need to Pkg.add("Plots") once you already have plots. After running that command once (ever) you only need using Plots

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Thank you very much, but I already made the changes and it still doesn’t work. I changed the expression of t to 0: 0.01: 10 and it didn’t work either.

should be

y = 0.2 .* cos.(2 .* t .+ π )


or equivalently

y = @. 0.2 * cos(2t + π)


Anyway the point is this has nothing to do with the Plot.jl package. I suggest you take a look at the julia manual to sort out syntactical issues.

By the way, I am using  and  to quote my code so it’s nice to read

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It worked! Apologies if it looked like I was blaming the package. I’m new to Julia and in the community maybe I chose the wrong tags. Thank you very much for your help.

Here, you need a .+ when adding a scalar to a vector, like 0.2cos.(2t .+ π), or as suggested by @tomerarnon, use @. 0.2cos(2t + π). Also note, there is no space after function names cos ( or between 0.2 cos. Finally, range can be written shorter as below.

using Plots

t = range(0, 10, length=100) # 0:0.01:2π
y = 0.2cos.(2t .+ π)

plot(t, y, label="cos(x)")
plot!(xlab="Time (s)", ylab="Distance (m)")

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Are these points included 0.2cos. (2t. + π) due to Broadcasting? And
can you explain to me the use of this macro @. 0.2cos (2t + π)?

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@. inserts a dot between all operators and function calls. If you are new to Julia, using the help system will be useful. Just start julia and enter ?@. and press enter.

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