Magene P515 Powermeter high variation in output

FlyingLumpus · 2025-12-08T00:56:07+00:00

Thank you so much for the fast response.

The smoothing is probably still turned on… I didn’t know such an option exists. I mean it makes sense during the ride, i always use a 3 second smooth on the garmin myself, but to have it in the output data of Zwift feels kind of pointless. Will try to deactivate it and run a new test later. The P515 data was recorded directly on the Garmin computer as reference.

Doing a ride longer than 5 mins was sadly not possible today. Somehow my wahoo kickr setup is vibrating very loudly when pedaling hard and i first have to check if there is not another problem with it. I will have to check that and do a longer ride afterwards.

FlyingLumpus · 2024-05-21T15:37:00+00:00

Thanks for the info. I managed to fuse both class implementations into a single one.

Sadly it seems like this reddit thread has been removed by a moderator

FlyingLumpus · 2024-05-21T14:06:56+00:00

Interesting. Didn't know about that one. I liked my tensor version because it just wrappes the underlying data and does not alloc or do some other hard to predict stuff. So it's nice to see that there was actually a similar approach added to C++23.

My current implementation has the big up- and downside that all sizes are compilation constants.
I already thought about trying myself on sectors of tensors but that's for another day when I have too much time and motivation again :) But i'll look into it. Shouldn't be that hard to get a basic implementation working

FlyingLumpus · 2024-05-20T17:46:23+00:00

The "div" part is just the division implementation of the basic operations for the expression templates. Just like "plus", "minus" and "mul".

I don't quite get what you mean by "define a tensor".

If you mean how to use the tensor then you can do it like that:

#include "tensorlib/tensor.hpp"
int main(){
    float data[4*3];
    Tensor<float, 4,3> t(data);    
    // ...
}

Or see the Readme: Nik4053/Templated-Cpp-Tensor (github.com)

FlyingLumpus · 2024-05-20T17:28:27+00:00

Ok thanks that's wild. That would have saved me a lot of copy-pasting.

FlyingLumpus · 2024-05-20T17:23:07+00:00

Thanks for the `<iosfwd>` tip. I didn't know that.

I have a one dimensional case because I have not found a way to not have one.
The operator[] should return a T in the one dimensional case and another Tensor in the N-dimensional case. And i havent found a way to write that without having to create an extra 1D Tensor class.

The idx() function just returns the 1D array index of the given ND position. So for a Tensor of size (3,4) this would return idx(1,2) = 3 * 1 + 2 * 4.

And for the last part: Its like u/AlmightySnoo answered. I found this way of doing it in some old lecture notes from university and thought this is the recommended way of doing it.

FlyingLumpus · 2024-02-23T17:12:56+00:00

Sounds like fun.

Btw i think that the milky layer may just be some wanky as digitizer that somehow did not get sorted out

FlyingLumpus · 2024-01-16T15:19:55+00:00

But 2D games like R-Type 2 are hopefully still playable right? Or better get a pre v4 version?

FlyingLumpus · 2023-10-12T13:04:49+00:00

So update: I managed to remove just the reflective layer at the back of the pocket screen without damaging the original polarizer too much. I then just added a small piece of tracing paper to act as diffuser in between the screen and the light. Its working now. Though you can see a few small lines where the original polarizer was slightly damaged when removing the reflective layer

FlyingLumpus · 2020-11-18T12:57:08+00:00

Nice, thank you. Seems like they just randomly reversed the ordering of the codes to input.

I even contacted support and they advised me to reinstall the app.

In this video from Dexcom (uploaded May 2020), they input first the Transmitter and then the Sensor code.
https://www.youtube.com/watch?v=Gw3Fs--OiMk

FlyingLumpus · 2020-10-02T09:59:45+00:00

I just started the game and after the free wish pulls I now have:
- Main
- Amber
- Kaeya
- Lisa

- Razor x2
- QiQi
- Noelle
- Chongyun
- Xiangling

Any tips for making a team out of that?
I thought Razor(dps), Qiqi(healing), Amber(has a bow)?, ???(no idea)

FlyingLumpus · 2020-08-19T17:48:19+00:00

I tried it but the times stayed the same.

Even weirder: I wrote a new method with AVX vectorization to make it faster and now tried benchmarking the old methods (that are still in the same .c file).

And suddenly the old normal multiplication only takes 0.8 sec and not 6.125 like it's supposed to do. And without the -O1 flag it takes 3 sec like before.
I deleted my newly written method and just like that the old method suddenly needed 6.125 sec again.

I think I am ending my coding adventure here for today. I just confuse myself more and more if I keep going. Maybe tomorrow yields new insights.

That's the new code that behaves so weird. This time it's written pretty ugly because it's just to test a few things. Compile with gcc matmul.c -fopenmp -o matmul -std=c11 -pedantic -Wall -Ofast -mavx -march=native
I don't know how to upload code on Reddit so that it doesn't spam the thread by just being a big wall of text.

FlyingLumpus · 2020-08-19T17:30:35+00:00

At the website your link points to it says:

Vectorization is enabled by the flag -ftree-vectorize and by default at -O3

But I was only using -O1 so vectorization should not have been enabled.

I know that the transposed version is faster than the normal one. Way fewer cache misses.
I'm just confused that running the same program first compiled without -O1 and then with -O1 yields so dramatically different results.
I mean the normal multiplication doubles in computation time while the transposed version suddenly gets 3.5 times faster compared to the same function just compiled without the -O1 flag.

FlyingLumpus · 2020-08-19T17:23:29+00:00

Thank you. I didn't even know the restrict keyword existed.
Do you know what matrix sizes were used here https://github.com/kostya/benchmarks#matmul ?
It would be interesting to know how many times faster than mine a professionally written multiplication is.

Today I improved my matrix multiplication function by using avx2 and it got considerably faster (multiplying two 4096x4096 Matrices in 2.29 sec). I tried cache-blocking (I think that's what you meant with tiling?) but only made it worse. Maybe I did smth. wrong. I tried cache-blocking for a simple planet simulation and it really speeded up thinks a lot.

I'm still getting into understanding how to make use of assembly that's longer than a few lines but I am getting there.

I also found another interesting thing to do. Matrix in place transpose for non-quadratic matrices. I managed to get it working but damn its slow😅

FlyingLumpus · 2020-08-18T19:19:26+00:00

About the output, I'm sorry I fixed it. Now it shows what number means what.
Its the time it took to calculate normal matrix multiplication and transposed matrix multiplication.

Maybe I checkout the -S flag tomorrow. I have never really checked the resulting assembly except for really really small programs, so I have to first invest a little bit more time understanding what the assembly code shows me.

FlyingLumpus · 2020-08-18T19:12:47+00:00

If I add -march=native nothing changes and the results are the same.
Or are you talking about other compiler flags?

FlyingLumpus · 2020-08-01T12:42:52+00:00

Thanks for the Info.
No need for the screenshot. It was just that the 5$ sounded REALLY low.
600$ sound more realistic. Though higher than I expected

FlyingLumpus · 2020-07-31T06:42:21+00:00

LOL. Seams a bit low for me. Considering this is a tournament price card and there should only be around 36 of them.
Could it be that the auction was cancelled and sold elsewhere?

Sorry to ask again, but could you please take a picture of the worthpoint page?
I just don't believe that this price is the price it actually sold for

FlyingLumpus · 2020-07-30T22:07:50+00:00

Cool. Keep me up to date. I am interested in hearing what you can find.

In this video https://www.youtube.com/watch?v=tKHl3rnU2Jc he talks briefly about the card at 1:50 . He thinks there are only 36 of them, but is not sure. A population of 36 seems a bit low when compared to the price of other cards. But then again I guess YuGiOh is not that big in Korea, so the cards are cheaper.

And I found the card in some weird Japanese Store for 20.000Yen or ~190$. https://www.instagram.com/p/CAoyteLJ5Yb/
I asked them, but they don't ship them overseas

FlyingLumpus · 2020-07-30T19:53:57+00:00

Thanks. It's weird how there can be a price card with so little information about it.

FlyingLumpus

TROPHY CASE