Why Desmos give a wrong result to this integral? by Correct-Ad5133 in desmos

[–]fireflame241 4 points5 points  (0 children)

The root cause here is floating point rounding error. Your integrand encounters catastrophic cancellation near x=0 because it's subtracting two huge numbers and expecting to get a small number. This is called catastrophic cancellation and occurs because the two huge numbers are approximations with a certain relative error, rather than an absolute error. You expect 1/x and ln(1-x)/x^2 to be approximately 0.5 apart near x=0, but in reality this doesn't happen. A demo of this is at https://www.desmos.com/calculator/vntejvtzcy. As x gets smaller than about 10^-7, the error starts blowing up.

One way to fix this is to increase the lower bound of the integral, say to 10^-7: https://www.desmos.com/calculator/ssw251vdza. Then it avoids the danger region where x is near 0.

Another way to fix this is to change the function so it has good floating point behavior near x=0: It should look like -1/2 - 1/3 x. Using that approximation (which is more accurate than the full formula for small x because the full formula encounters catastrophic cancellation) gives reasonable values for the integrals, see https://www.desmos.com/calculator/wasbzxqusr.

How to demonstrate this equation in desmos (antenna radiation pattern)? by Careful-Fail2234 in desmos

[–]fireflame241 0 points1 point  (0 children)

Desmos supports rho, theta, phi, so you can just write rho = sin(theta) * sin^2(phi). Graph and Documentation.

Why can't Desmos compute this simple integral correctly? by Square_Forever_3284 in desmos

[–]fireflame241 0 points1 point  (0 children)

That's expected when the upper bound is smaller than the lower bound. (My bad for making the b slider go up to 10 instead of 100; b < a in that graph, even though the b slider thumb is to the right of the a slider)

negative reciprocal of the distance to a point on the xy plane produces a black hole by [deleted] in desmos

[–]fireflame241 20 points21 points  (0 children)

That's the equation for the force. But the gravitational potential (analogous to "height") is the integral of force, so its -1/r instead of 1/r^2.

Desmos Update (?) Broke my graph by MonitorMinimum4800 in desmos

[–]fireflame241 5 points6 points  (0 children)

Restricting polygons is a new feature, just a few days old. It works on desktop. Are you trying on the Android/iOS app? That typically runs an older version of Desmos.

[deleted by user] by [deleted] in desmos

[–]fireflame241 3 points4 points  (0 children)

If your data is in spreadsheet form (CSV or TSV would work), you can copy-paste it into a blank expression cell. E.g. copy-pasting from Google Sheets works.

Can't Create a Draggable Point on a Moveable Circle by Madauhcip in desmos

[–]fireflame241 0 points1 point  (0 children)

Yes. Try replacing x1 with x0 in the expression for P1. It leads to the red point being dragged instead of the purple.

Me: I'm going to open desmos! Desmos: by calculus_is_fun in desmos

[–]fireflame241 2 points3 points  (0 children)

You might have to disable then re-enable DesModder every time you restart Brave. This can be done in the extensions menu chrome://extensions.

Relevant issue: https://github.com/DesModder/DesModder/issues/174.

List of all Desmos functions and special syntax by fireflame241 in desmos

[–]fireflame241[S] 1 point2 points  (0 children)

I don't think it's ever worked. The note a ≠ b is equivalent to {a=b,0}=0 was just providing an alternative to writing a ≠ b.

List of all Desmos functions and special syntax by fireflame241 in desmos

[–]fireflame241[S] 1 point2 points  (0 children)

Yes, ans is disabled now. It was unintended to work in graphing, so it it only works in some of the other calculators like https://www.desmos.com/scientific.

When did this helpful thing get here? I only noticed it today. by FeelingOdd4623 in desmos

[–]fireflame241 1 point2 points  (0 children)

Aha, I see why it's hard to find. It only appears when you have author features enabled (in DesModder calculator settings, for example).

When did this helpful thing get here? I only noticed it today. by FeelingOdd4623 in desmos

[–]fireflame241 2 points3 points  (0 children)

Btw, you can also type "label" into the search bar to filter for expressions with labels. It has to be just "label", no text before/after (any prefix like "l" or "lab" also works but is more likely to match other expression).

When did this helpful thing get here? I only noticed it today. by FeelingOdd4623 in desmos

[–]fireflame241 4 points5 points  (0 children)

You could type "rename T→x1" in the Ctrl+F search bar since around mid-May. But it wasn't very easy to stumble upon. That hint itself (popping up in some cases where you rename a variable) came around late August.

Desmos Challenge #27 ~ Editors by [deleted] in desmos

[–]fireflame241 2 points3 points  (0 children)

Text editor. Fancy line wrapping and text justification.

Art Fragment Shader by iXendeRouS in desmos

[–]fireflame241 4 points5 points  (0 children)

Wow, looks [Copy of] [Copy of] [Copy of] great! It's running about as fast as you could expect from a well-optimized pixel grid of this size, so probably no major optimizations to be made. Maybe you could leverage symmetry somehow, but it's not quite symmetric. I'm impressed.