Assign x values is plots

General Usage
1 
using Roots
using Plots

J=f(x)=x^2+10sin(x)
g(x)=f(x)-1000
find_zeros(g,0,10000)

plot(J)

The above works fine, but I want to plot a horizontal line at 1000, and plot J, so that x goes from 0 to 100. I’m not sure from the documentation, how to assign 0 values

2

something like

using Roots
using Plots

J=f(x)=x^2+10sin(x)
g(x)=f(x)-1000
find_zeros(g,0,10000)

plot(J, 0, 100)
hline!([1000])

?
I’m not really sure, what you mean by

how to assign 0 values

Assign them to what?

1 Like
3

to x, I want to assign a range of 0, 100 to x, so that it shows x for that range. Which is exactly what you provided! Thanks!

1 Like
4

Nice function find_roots.

You don’t need to name the function by J, unless there is another reason for introducing it.

I played with a modification of your problem:

using Plots, LaTeXStrings, Roots
f(x) = (x/4)^2 +10sin(x+pi/3)
g(x) = (x/5)^2
h(x) = f(x)-g(x)
xr = find_zeros(h,0,20)
#
hline(f.(xr),lw=4,lc=:orange,la=0.15,label="")
vline!(xr,lw=4,lc=:orange,la=0.15,label="")
plot!(f,0,20,lw=3,lc=:cornflowerblue,label=L"f(\cdot)")
plot!(g,0,20,lw=3,lc=:crimson,label=L"g(\cdot)")
scatter!(xr,f.(xr),ms=7,mc=:orange,label="roots",legend=:topleft)

which produces:

image
image1748×1186 157 KB

Julia is nice :-). I love the support of html colors, see, e.g., HTML Color Names .

3 Likes
5

I thought I dod for plots, but it looks like you assign values for plots. I like the graph, but the big thing is to show that since f(x) is continuous, there is value for every point, even irrationals, like sqrt(1000)

6

What is LaTexStrings? I think I need to work more with LaTex, I’ve gotten handy with the equation functions in Word.

7

It’s not clear what you want to show. Could you please be more specific?

8

Just the that that f is the function f(x) when plotting. I changed it in Julia afterwards.

9

Package LaTeXStrings allows for a modifier (L) placed in front of strings ("..."), e.g., L"...", which inserts some \LaTeX code and makes it simpler to construct strings with math. So I can write L"f(\cdot)" which the LaTeXStrings package changes to the appropriate string of \LaTeX code.

To appreciate LaTeXStrings, you need to find a book on \LaTeX/\TeX math, and study the documentation of LaTeXStrings.

LaTeXStrings is not perfect, essentially because \LaTeX uses symbol $ to bracket math, while $ is simultaneously used in Julia as “interpolator” in text strings. I don’t have any perfect solution to this, though.

1 Like
10

You want the function nameof giving the name of a function

julia> function g(x)
       x + 1
       end
g (generic function with 1 method)

julia> function myplot(fun, x)
           plot(fun.(x), label = string(nameof(fun)))
       end
myplot (generic function with 1 method)

julia> x = [1, 2, 3];

julia> myplot(g, x)
2 Likes
11

Yes, I want to study LaTex, but I’m in a rush to study everything.

1 Like