Processing 1.0 - Processing Discourse - push data through a matrix

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push data through a matrix (Read 2444 times)

kspksp

push data through a matrix
Dec 21^st, 2009, 8:59am

I want to move data in a matrix.
As you see in the code down here i do it field by field (z[i][j]=z[i][j-1])
It works, but it doesn’t seem to be very efficient. Sad

Is there a Lib or some commands to do this in a faster or maybe just in an easier way?

Thank you and merry Christmas!

Code:

void moveit(){
  for(int i=0;i<B;i++){
    for(int j=L-1;j>0;j--){
      z[i][j]=z[i][j-1];
    }
  }
}

JR Full Member Offline Posts: 149	Re: push data through a matrix Reply #1 - Dec 21^st, 2009, 9:15am I don't think there are many ways of doing it more efficiently than this. Unless you are going to use processor specific instructions or if you are going to assume that the matrix is from a specific type (sparse, ..). Can you tell us more about the size, usage and contents of the matrix?

kspksp YaBB Newbies Offline Posts: 22	Re: push data through a matrix Reply #2 - Dec 21^st, 2009, 9:42am Matrix is [1024 x 150]. I put FFT data in the first line and render the whole matrix to an fft-diagram. The diagram should scroll forward one step per loop. The matrix is an float array (float [][] z = new float[1024][150]; )

PhiLho

Re: push data through a matrix
Reply #3 - Dec 21^st, 2009, 10:35am

The only possible optimization I see (while using plain array) is to change access to array so it wraps around.
The idea is to set an origin in the array. Instead of access [0], you access the origin, and at [n] you access origin+n or n-arrayLen if you overflow (if origin+n>arrayLen).
Not sure if there is a real gain of speed if you do lot of access vs. shift rate (vs. array size). The only way to know is to test and see if there is an improvement!

Another way is to use a Java Collection: it will cost memory but shifting will do only a couple of reference changes.

JR Full Member Offline Posts: 149	Re: push data through a matrix Reply #4 - Dec 21^st, 2009, 1:15pm Indeed, something like a linked list (http://java.sun.com/j2se/1.4.2/docs/api/java/util/LinkedList.html) would work well here.

PhiLho YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: push data through a matrix Reply #5 - Dec 22^nd, 2009, 1:52am Or a Queue.

JR Full Member Offline Posts: 149	Re: push data through a matrix Reply #6 - Dec 22^nd, 2009, 2:05am PhiLho wrote on Dec 22^nd, 2009, 1:52am: Or a Queue. A Queue is an interface, and LinkedList implements it.

PhiLho YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: push data through a matrix Reply #7 - Dec 22^nd, 2009, 2:42am You are right! I was more thinking of ArrayDeque (Java 1.6 only!), said to be "faster than LinkedList when used as a queue". But anyway, I think my idea of movable origin in a plain array is probably faster, avoiding boxing/unboxing. But a little harder to write, debug and understand...

JR Full Member Offline Posts: 149	Re: push data through a matrix Reply #8 - Dec 22^nd, 2009, 2:51am Yup, good point. And yeah, a moving origin is definitely the faster way to go, but it produces more difficult code and speed gain isn't that great i think. I'm not sure though

kspksp

Re: push data through a matrix
Reply #9 - Dec 22^nd, 2009, 8:56am

Thank you guys,
i check the idea of movable origin, still got no idea how it works...but i will work it out.
Meanwhile i did some improvements to my code...precalc the Lin->dB stuff bla bla bal...it helps a lot because the log() thing sucks a lot of power on this big array.

btw: i work on a thing like this http://www.youtube.com/watch?v=bII9fjpnZ6k&NR=1...but much prettier! Wink

Re: push data through a matrix
Reply #10 - Dec 22^nd, 2009, 9:45am

I have not tested it and it is not complete, but it shows the general idea:

Code:


class FFTRingBuffer
{
  float[][] fftData;
  int origin;
  
  public FFTRingBuffer(int fftSize, int bufferSize)
  {
    fftData = new float[bufferSize][fftSize];
  }
 
  void add(float[] fft)
  {
    fftData[origin] = fft;
    origin = (origin+1)%bufferSize;
  }
  
  float get(int i, int j)
  {
    return fftData[(origin+i)%bufferSize][j];
  }
}

kspksp

Re: push data through a matrix
Reply #11 - Dec 23^rd, 2009, 11:06am

Hi JR,

What means the "%" in the syntax?
Origin = (origin+1)%bufferSize;

I’m not really sure if i get it...but does this idea "move" the date?
If i name the fft i put into the array fft0(x) (x=position in the array) i want to move the date like this:
step 0: fft0(0)
step 1: fft0(1);fft1(0)
step 2: fft0(2);fft1(1);fft2(0)

Or is it like this:
data is put in the array at counting up position:
fft1;fft2;fft3;fft4;fft5;.....;fftn
and it just translate the beginning position of the diagram:
step 0: plot from 0 to fftsize
step 1: plot from 1 to fftsize+1
step n: plot from n to fftsize+n
if the plot reaches the end of the array it starts at the beginning again.

I like the 2nd idea, because i don’t have to move data...just move the origin of the diagram...make sense...did you mean this?

PhiLho YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: push data through a matrix Reply #12 - Dec 23^rd, 2009, 2:15pm kspksp wrote on Dec 23^rd, 2009, 11:06am: What means the "%" in the syntax You can find % (modulo) by searching % in the Language reference index page.

JR Full Member Offline Posts: 149	Re: push data through a matrix Reply #13 - Dec 23^rd, 2009, 3:35pm kspksp wrote on Dec 23^rd, 2009, 11:06am: I like the 2nd idea, because i don’t have to move data...just move the origin of the diagram...make sense...did you mean this Exactly

kspksp

Re: push data through a matrix
Reply #14 - Dec 25^th, 2009, 11:05am

I did the changes...and it runs pretty well! Cheesy

Now i got a new problem...the rendering of the 102400 faces needs to much cpu...or gpu...don't care (2^10*100 faces=102400 -> 2^10=1024=fftsize, 100=Buffersize)..i use Opengl...but ok..thats another story..

Thank you guys for the tip, specially JR!

Merry Christmas and a happy new year!

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