[Scilab-users] Peaks and positions

[Samuel Gougeon]

Le 26/01/2013 17:00, constantina a écrit :
> Sorry, I know is a basic question, i now the answer in matlab but not in
> scilab.... What is the function that let me find "peaks " in a matrix and
> the position of the peaks???
Here is a possible solution, including peaks on the borders:

m = rand(6,6)
M = [m(2,:) ; m ; m($-1,:) ];
M = [M(:,2)  M  M(:,$-1)];
pC = M(2:$-1,2:$-1)>M(1:$-2,2:$-1) & M(2:$-1,2:$-1)>M(3:$,2:$-1);
pR = M(2:$-1,2:$-1)>M(2:$-1,1:$-2) & M(2:$-1,2:$-1)>M(2:$-1,3:$);
isPeak = pC & pR
find(isPeak)      // returns linearized indices of peaks
m(~isPeak) = 0 //  to show only peaks

giving:

-->m = rand(6,6)
  m  =
     0.0437334    0.7783129    0.8415518    0.5618661 0.3873779    
0.2615761
     0.4818509    0.2119030    0.4062025    0.5896177 0.9222899    
0.4993494
     0.2639556    0.1121355    0.4094825    0.6853980 0.9488184    
0.2638578
     0.4148104    0.6856896    0.8784126    0.8906225 0.3435337    
0.5253563
     0.2806498    0.1531217    0.1138360    0.5042213 0.3760119    
0.5376230
     0.1280058    0.6970851    0.1998338    0.3493615 0.7340941    
0.1199926

-->M = [m(2,:) ; m ; m($-1,:) ];
-->M = [M(:,2)  M  M(:,$-1)];
-->pC = M(2:$-1,2:$-1)>M(1:$-2,2:$-1) & M(2:$-1,2:$-1)>M(3:$,2:$-1);
-->pR = M(2:$-1,2:$-1)>M(2:$-1,1:$-2) & M(2:$-1,2:$-1)>M(2:$-1,3:$);
-->isPeak = pC & pR
  isPeak  =
   F F T F F F
   T F F F F F
   F F F F T F
   F F F T F F
   F F F F F T
   F T F F T F

-->find(isPeak)      // returns linearized indices of peaks
  ans  =
     2.    12.    13.    22.    27.    30.    35.

-->m(~isPeak) = 0 //  to show only peaks
  m  =
     0.           0.           0.8415518    0. 0.           0.
     0.4818509    0.           0.           0. 0.           0.
     0.           0.           0.           0. 0.9488184    0.
     0.           0.           0.           0.8906225 0.           0.
     0.           0.           0.           0. 0.           0.5376230
     0.           0.6970851    0.           0. 0.7340941    0.


Regards
Samuel


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