The link that takes one to the summary of the course materials seems to be not working

I get this error when i try to run 02-covid_data.jl in Pluto. I thought I was just missing a Pkg.add() but it seems plot() used to be available in earlier versions of Julia, but has been deprecated for quite a while, and I am not sure where the plot() should be coming from. (In the course website you write that you are using Julia 1.5.1.)

https://www.bonfire.com/introduction-to-computational-thinking-shirt/

I have started following the course, and read through the first two notebooks. In both I get the following error that disables some of the code examples in the notebooks:

Failed to show value:

MethodError: no method matching length(::Nothing)

Closest candidates are:

length(!Matched::BitSet)

@ Base bitset.jl:348

length(!Matched::Base.AsyncGenerator)

@ Base asyncmap.jl:390

length(!Matched::RegexMatch)

@ Base regex.jl:285

...

Stack trace

Here is what happened, the most recent locations are first:

    _similar_shape(itr::Nothing, ::Base.HasLength) @ [array.jl:710](https://github.com/JuliaLang/julia/tree/bd47eca2c8aacd145b6c5c02e47e2b9ec27ab456/base/array.jl#L710)
    _array_for(::Type{Core.MethodInstance}, itr::Nothing, isz::Base.HasLength) @ [array.jl:726](https://github.com/JuliaLang/julia/tree/bd47eca2c8aacd145b6c5c02e47e2b9ec27ab456/base/array.jl#L726)
    _method_instances(f_type::Any, t_type::Any) @ Tricks.jl:136
    #s1#1 @ Tricks.jl:20
    var"#s1#1"(T::Any, ::Any, f::Any, t::Any) @ 
    (::Core.GeneratedFunctionStub)(::UInt64, ::LineNumberNode, ::Any, ::Vararg{Any}) @ boot.jl:602
    content(x::HypertextLiteral.Result) @ convert.jl:91
    show(io::IOContext{IOBuffer}, m::MIME{Symbol("text/html")}, toc::PlutoUI.TableOfContentsNotebook.TableOfContents) @ TableOfContents.jl:502

import Pkg
Pkg.activate(mktempdir())
Pkg.add([
Pkg.PackageSpec(name="Images", version="0.22.4"),
Pkg.PackageSpec(name="QuartzImageIO"),
Pkg.PackageSpec(name="PlutoUI", version="0.7"),
Pkg.PackageSpec(name="HypertextLiteral", version="0.5"),
Pkg.PackageSpec(name="ForwardDiff"),
Pkg.PackageSpec(name="NonlinearSolve"),
Pkg.PackageSpec(name="StaticArrays")
])

this cause a lot of problem, when opening the notebook every time it shows I need to add another packages, even though the packages do exists, these lines acutually does not add any packages to Julia, so it makes opening the notebook a pain.

Could you please do not add those lines in Notebook?

Thanks in advance

This page: https://computationalthinking.mit.edu/Fall20/installation/

Looks fine on GitHub but on the website literal HTML entities are shown.

For example:

The link at the end of the readme file
https://github.com/mitmath/computational-thinking/blob/578736f39c6eeb388ff5c51f9f28f0b8d8f29670/README.md
points to the Spring21 version instead of the latest version.

# Go to [computationalthinking.mit.edu](https://computationalthinking.mit.edu/Spring21/) to learn more!

should be

# Go to [computationalthinking.mit.edu](https://computationalthinking.mit.edu/) to learn more!

I couldn't find any usage of it. Just wondering if it is needed? (seems to run without issues without it)

Not a real issue.
The url referenced by a hint "In Section 1.1, we drew a red square on top of the image Philip with a simple command..." leads to a 404 "File not found" page.

I think a picture does better here

If I go to HW0 and click "set up Julia and Pluto"

then weirdness ensues

Yet if I copy and paste the link into my browser, it works fine

I suspect this is an issue with the plutonotebookpage styling?

Hi, all,

The invite link for Discord is expired. Could you help to create a new one?

THX!

Hi,

I am preparing a course based on Pluto notebooks and I would like to base some of the material on notebooks from this repo. Since there is no license in this repository, would you mind clarifying under which conditions I can reuse some of the material?

In particular, I would like to use your install instructions, the hw0.jl and the notebook on basic syntax.

Best,
Fabian

Hi, based on the discussion in the class discord (copied below), should these conditionals be switched/tweaked?
https://github.com/mitmath/18S191/blob/1dddcc9cb2cb88dce5fb17dea23b67a7e70da9b7/homework/homework6/hw6.jl#L818-L821

I.e., to something like this?

if result ≈ 1462
	correct()
elseif result ≈ 6358
	almost(md"Use ``f'(a)``, not ``f'(a+h)``.")

Copied from discord server:

user1 Yesterday at 11:22 AM
Hi guys, silly question, but why in the Euler step they make us use:

Use f'(a+h) instead of f'(a)?

I've tried to infer it geometrically, but I get lost in the approximation details - does someone has a video/resource that explains the rationale behind this trick to improving accuracy?

Is it just because we're integrating 'forward' ?

IanWeaver Yesterday at 6:50 PM
Oh, I totally missed that! Thanks for pointing that out, I think they might have just hard-coded the wrong branches in the test, but this would definitely be something worth following up with the instructors about. For example, I think 6358 and 1462 might be switched, and that the almost message should read "Use f'(a), not f'(a + h)." instead. The later implementations of this method also look to agree with this.

There are certainly different numerical methods though where you can use the slope at different points, RK4 probably being the most famous example. You can also just use the slope at the end of the step, but that would then turn it into an implicit scheme known as backward Euler. In general, this would require a root-finding method or fixed-point iteration to solve. If you happen to be interested in those kinds of methods, I made a brief write up about it here, but I haven't updated that package in a while:
https://spacejam.readthedocs.io/en/latest/background.html#background

One of the nice things about implicit methods is how stable they are, but I think that is outside the scope of this homework assignment, which is another reason why I think the above problem you brought up might just be a typo.

Finally, for a quick intro to numerical methods, you can't beat the OGs:
https://www.youtube.com/watch?v=RGtCw5E7gBc
https://www.youtube.com/watch?v=q87L9R9v274(edited)
[6:53 PM]
I'll go ahead and open an issue about this and link to the discussion here 
Link to issue: #61

user2 Yesterday at 7:04 PM
yea, i was also weirded out by that because they used f'(a) in the preceding equation

Failed to load notebook
The file D:\Julia SoftWare\18S191 SUBMISSION\hw0 (1).jl could not be loaded. Please report this error!

Go back

Error message:

File is not a Pluto.jl notebook
Stacktrace:
[1] error(::String) at .\error.jl:33
[2] load_notebook_nobackup(::IOStream, ::String) at C:\Users\user.julia\packages\Pluto\qC4PK\src\notebook\Notebook.jl:113
[3] #8 at C:\Users\user.julia\packages\Pluto\qC4PK\src\notebook\Notebook.jl:164 [inlined]
[4] open(::Pluto.var"#8#9"{String}, ::String, ::Vararg{String,N} where N; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at .\io.jl:325
[5] open at .\io.jl:323 [inlined]
[6] load_notebook_nobackup(::String) at C:\Users\user.julia\packages\Pluto\qC4PK\src\notebook\Notebook.jl:163
[7] load_notebook(::String) at C:\Users\user.julia\packages\Pluto\qC4PK\src\notebook\Notebook.jl:180
[8] open(::Pluto.ServerSession, ::String; run_async::Bool) at C:\Users\user.julia\packages\Pluto\qC4PK\src\webserver\SessionActions.jl:16
[9] open at C:\Users\user.julia\packages\Pluto\qC4PK\src\webserver\SessionActions.jl:10 [inlined]
[10] (::Pluto.var"#try_launch_notebook_response#96"{Pluto.var"#try_launch_notebook_response#85#97"{Pluto.ServerSession}})(::String; title::String, advice::String, home_url::String) at C:\Users\user.julia\packages\Pluto\qC4PK\src\webserver\Static.jl:63
[11] (::Pluto.var"#serve_openfile#99")(::HTTP.Messages.Request) at C:\Users\user.julia\packages\Pluto\qC4PK\src\webserver\Static.jl:92
[12] handle(::HTTP.Handlers.RequestHandlerFunction{Pluto.var"#serve_openfile#99"}, ::HTTP.Messages.Request) at C:\Users\user.julia\packages\HTTP\atT5q\src\Handlers.jl:253
[13] handle(::HTTP.Handlers.Router{Symbol("##253")}, ::HTTP.Messages.Request) at C:\Users\user.julia\packages\HTTP\atT5q\src\Handlers.jl:467
[14] (::Pluto.var"#190#196"{Pluto.ServerSession,HTTP.Handlers.Router{Symbol("##253")}})(::HTTP.Streams.Stream{HTTP.Messages.Request,HTTP.ConnectionPool.Transaction{Sockets.TCPSocket}}) at C:\Users\user.julia\packages\Pluto\qC4PK\src\webserver\WebServer.jl:123
[15] handle at C:\Users\user.julia\packages\HTTP\atT5q\src\Handlers.jl:269 [inlined]
[16] #4 at C:\Users\user.julia\packages\HTTP\atT5q\src\Handlers.jl:345 [inlined]
[17] macro expansion at C:\Users\user.julia\packages\HTTP\atT5q\src\Servers.jl:367 [inlined]
[18] (::HTTP.Servers.var"#13#14"{HTTP.Handlers.var"#4#5"{HTTP.Handlers.StreamHandlerFunction{Pluto.var"#190#196"{Pluto.ServerSession,HTTP.Handlers.Router{Symbol("##253")}}}},HTTP.ConnectionPool.Transaction{Sockets.TCPSocket},HTTP.Streams.Stream{HTTP.Messages.Request,HTTP.ConnectionPool.Transaction{Sockets.TCPSocket}}})() at .\task.jl:356

Hi,

Just wanted to let you know that the test for the answer to Ex 3.5 in Hw1 doesn't appear to be working properly. I get a correct answer for the following (obviously wrong) code:

function noisify(x::Number, s)
	rand_num = rand()
	noisy_num = x + rand_num
	noisy_num = clamp(noisy_num, 0., 1.)
	return noisy_num
end

Afraid I'm not not sure how to fix it though.

I feel like the check might be inadequate?

https://github.com/mitmath/18S191/blob/123040947d5b03a572b58c261b3009c8041b5c4e/homework/homework1/hw1.jl#L986-L1000

Since it is checking 0.3, floor with any digits ≥ 1 will pass, when really we want digits=1.

Neither via copying the link on the MIT OCW page and pasting it to Pluto nor copying directly the link to the .jl file is working, as Pluto seems to not recognize it as a notebook.
I'm not quite sure what the problem really is.

When I try to watch Lecture 4 from Denmark.
YouTube just gives the message: "This video is not available in your country"

@fonsp I can take a shot at this unless you would rather do it

For week 1 in Exercise 2.3 the student is required to write a function to quantize instances of subtypes of AbstractRGB e.g. RGB. The live docs imply that the functions red(c) green(c) and blue(c) can be used to "pull out" the RGB values from a pixel.

However, the function red(c) is overwritten by a later variable assignment to red on L301

https://github.com/mitmath/18S191/blob/14ca6fa5178f5c0025c5e845c7c40b7ea219d0dd/homework/homework1/hw1.jl#L301

This causes an error to be displayed if the student assumes that red is a function, and tries to call it

Commenting out the variable assignment reverts the function override

I suggest that the variable red should be renamed to something like color_red to avoid overriding the function

Summary

Add a button to hide the sidebar on website

Details

• The sidebar on the course website takes huge space.
• This is okay for normal usage,
• but when used in split screen mode with terminal on the side for following alogn with, then it becomes troublesome
• as sidebar leaves very little space for the actual content.

Reference: Sidebar of youtube can be toggled full size, vs collapsed.

Screenshots

Versions

• Last modified: May 11, 2022
• Commit: 3481208

https://twitter.com/MITCompThinking

When run inverse_climate_model notebook, the following error appeared above the add and using package block.

Failed to precompile Plots [91a5bcdd-55d7-5caf-9e0b-520d859cae80] to /Users/.julia/compiled/v1.6/Plots/jl_iDFh4p.
error(::String)@error.jl:33
compilecache(::Base.PkgId, ::String, ::Base.PipeEndpoint, ::Base.PipeEndpoint)@loading.jl:1360
compilecache(::Base.PkgId, ::String)@loading.jl:1306
_require(::Base.PkgId)@loading.jl:1021
require(::Base.PkgId)@loading.jl:914
require(::Module, ::Symbol)@loading.jl:901
top-level scope@Local: 13

Hi everyone,

I'm sorry to open this issue here on GitHub but there seem to be not many people active on the Discord server at the moment.
I am wondering if MIT will hold the course in Fall21.

Thanks!

I cannot scroll on the lefthand sidebar. So Homework 2 isn't visible until I go fullscreen or use a device with a portrait mode.

Normal screen

Fullscreen

Which GitHub do you mean? The website?

I think raw versions of the hw links need to be used if you want people to be able to indeed download the files by right clicking.

e.g.,
https://github.com/mitmath/18S191/raw/master/homework/homework0/hw0.jl
or
https://raw.githubusercontent.com/mitmath/18S191/master/homework/homework0/hw0.jl
for hw0, instead of
https://github.com/mitmath/18S191/blob/master/homework/homework0/hw0.jl

@fonsp: Symbolic expansion isn't working on the published version. Maybe it just needs regenerating with a current version of Symbolics.jl?

Hi, I am running Pluto in chrome on windows 10 and get following error on the third code block. Is it possible to run the code on windows? curl.exe is installed.
failed process: Process('C:\WINDOWS\System32\curl.exe' -s -S -g -L -f -o 'C:\Users\ruper\AppData\Local\Temp\jl_2fRSvgqCWA' https://cdn.shortpixel.ai/spai/w_1086+q_lossy+ret_img+to_webp/https://wisetoast.com/wp-content/uploads/2015/10/The-Persistence-of-Memory-salvador-deli-painting.jpg, ProcessExited(35)) [35]

[email protected]:525[inlined]
download_curl(::String, ::String, ::String)@download.jl:44
[email protected]:62[inlined]
download(::String)@download.jl:89
top-level scope@Local: 17[inlined]

https://github.com/mitmath/18S191/blob/a4868df2420d9488b87af1eec0f6e3b0f654f6bd/notebooks/week10/time_stepping.jl#L57

Not strictly an issue; I just thought this may be useful to others. Also not an expert in Julia so if there's an easier way to do this please do correct the script.

I wanted to access the notebooks offline but due to Pluto installing packages per notebook, each notebook must be instantiated while having internet access. This script does that for every notebook in the notebooks directory in the Spring21 branch:

using Glob
import Pluto
import Pkg

function main()
  dirs = glob("./week*/*.jl")
  for jl_file in dirs
    println(jl_file)
    Pluto.activate_notebook_environment(jl_file)
    Pkg.instantiate()
  end
end

main()

This will help with discoverability for certain contents

In section 1.6 on newton method, in the 2D implementation the julia code doesn't match the latex equations.
The new approximation is defined to be x1 = x0 + δ, but in the julia function it's written as return x0 - δ.
This works in the code because in the definition of δthe minus sign is also missing, so practically it doesn't matter (they cancel out). However, I think it would be more intuitive if the code matched the latex equations

Redirect the http to https for the computationalthinking.mit.edu URL. Or click "Enforce HTTPS" in settings.

Also, update the URL for the class on the repo.

cc @christopher-dG

See here: https://computationalthinking.mit.edu/Fall20/lecture26/#what_is_a_discrete_fourier_transform and then look at the difference on YouTube

When I read the notes, I found this typo - "need too" should be "need to".

The link is https://computationalthinking.mit.edu/Fall23/climate_science/odes_and_parameterized_types/.

On the paragraph This says that "the way to...

Same problem as in #68

https://github.com/mitmath/18S191/blob/20c384d1a35547b5ce95ab2d01d1a0a1a7bfe940/src/images_abstractions/images.jl#L424

It looks like much of the content on the readme and index page are the same. This may lead to confusion for those making website updates.