mathy | using computer algebra systems to solve math problems | Math library

The problem is with the pointer assignments as you build the slice you are trying to reference. The addresses keep changing.

Is floating point math more precise for values close to unity?

Not really.

In general, floating point math well preserves realtive precision for *, /, sqrt() cover the lion’s share of the floating point range. +, - are subject to significant loss of relative precision (to the result) due to subtraction of nearby values.

Overall, there is little difference for normal numbers for relative precision. It varies from (0.5 to 1.0] * 2^-53.

The absolute precision changes in steps for powers of 2.

Floating point numbers [0.5...1.0) have the same absolute precision. For double 2^-54.
Floating point numbers [1.0...2.0) have the same absolute precision. For double 2^-53.
Floating point numbers [2.0...4.0) have the same absolute precision. For double 2^-52.
Floating point numbers [4.0...8.0) have the same absolute precision. For double 2^-51.
etc.

floating point arithmetic has the greatest precision if the numbers operated on are close to 1.0 (or sometimes 0.1). Is there any truth to this?

Values just under a power-of-2 have a higher absolute precision (by about 2x) than values just above a power of 2.

With tiny subnormal values, precision is lost, a bit per power of 2 until 0.0 is reached.

Advanced: Trig functions has a special concern when their magnitude is large. A high quality sin(1e10) does an internal extended high precision argument reduction to the primary [-pi ... pi] range. Not all trig function implementations handle this step well. So for radians arguments, starting in the primary range is useful to maintain precision. For degree arguments, a simple fmod(deg, 360.0) is a simple and precise range reduction.

The top three reviews are loaded as part of the HTML but the rest are loaded by javascript. Which is why you're only getting the first three results.

I'm not entirely sure whether this is the whole code you have for using scrapy. I'd be interested in why you choose that part of scrapy.

So deaing with javascript is a huge part of web scraping modern websites. I'm not entirely sure whether you're primarily using scrapy to webscrape. There are a few options to handle javascript with scrapy though.

First knowing that websites these days grab information on the fly, using javascript to invoke HTTP requests, called an AJAX request (Asynchronous Javascript and XHTML). This makes either a post or get HTTP request to an API/server and that HTTP response gives back information. In this case, they have preloaded 3 results into the HTML but asked for the rest of the reviews on loading the page with javascript.

In general there are two ways to deal with javascript orientated websites.

1. Re-engineer the HTTP requests - This is the most efficient way to get the data you want. You want to mimic these HTTP requests that javascript is invoking. If you can do that and this sometimes requires you to post headers, parameters and cookies then you can get the data you want.
2. Using some form of browser automation. Selenium is the package of choice, although never meant to be used in this way originally. It's slow, inefficient and brittle if using larger datasets.

For your particular website, you can re-engineer the HTTP requests to get the information you want. This is the ideal situation.

But how did I know that? Well one of the things you can do in chrome is turn off javascript. You have to inspect the page and go to the settings (click the three dots on the very right hand side of the page -> more tools -> settings). Refresh the page without javascript. You'll see there is only three reviews to see.

To understand what's happening using the ChromeDev Tools is very informative. If you go to the network tab when you right-click and inspect the page you'll see all the requests and responses made of the server. Going to the XHR tab is where you will find requests made that has the data you want. Here you have a bunch of requests and the responses.

See the pic below, I've inspected the page, gone to network and refreshed the page. This records the activity of the browser's requests and responses.

You can see there are about 6 requests, 5 GET requests and one POST requests. If you click each request you'll see a pop up box on the right hand side with the request data, preview and response.

Here I've clicked the first request, I've clicked preview, and you can see if you click through that there's some reviews.

I can see in the HTTP request for that data there's an offset of 10, which means it's grabbing the next 10 requests.

So I'm going to alter that offset to see if I can get the first 10 and then the second 10 (There's 20 reviews on this page).

Without having to manually input the parameters and headers etc... You can copy the request into a CURL. This can then be converted using a site like curl.trillworks.com into a nice python format.

Now it's worth while looking at the preview data, because you're going to have to use requests to process this. You're going to end up with a JSON object, you can tell this from the accept part of the HTTP get request is application/json.

So having copied this request into curl.trillworks.com. We have the below.

Here is an alternative recursive/backtracking approach:

Ok, I found the answer by way of suppressing outputs:

Just put this at the top of your second notebook:

I find the STIX fonts to be acceptable substitutes for computer modern.

This should do the trick:

The code you posted only calls gl.drawXXX one time in main so it's never going to draw anything ever again.

You have things set up so when the mouse is pressed click will be called but click never calls gl.drawXXX

Further, every time click is called you make a new buffer with a new set of points. That is not the normal way to use WebGL. The normal way is to setup your points once (once per thing you want to draw) and then use matrices to change position, orientation, scale.

I suggest you read some other tutorials on WebGL. This one kind of does what you're doing now but it follows up with how to change position, orientation, and scale, followed by how to do it with matrices for more flexibility. It also covers drawing multiple things

In any case to fix your code as is you need to draw after changing the vertices

you must be instead of primary_navigation use ->PrimaryNavigation(as defined in your relationship)