spmax

Below is a demonstration of the features of the spmax function

Contents

clear; close all; clc;

Syntax

[maxVal,maxInd]=spmax(A,B,dim,nanflag,logicRelevant,nanOut);

Description

This function is like the max function but is designed for sparse arrays. In particular it allows one to "ignore zeros" in the determination of the maxima.

Examples

Create example matrix

i=[2 1 1 2  2 3  3 4 4 5  5 5 6 6 7 8];
j=[1 1 2 3  4 5  6 7 8 9 10 11 12 13 13 13];
s=[-1 3 1 2 -1 1 -2 5 5 -1 0 2 3 10 11 NaN];
siz=max([i(:);j(:)]+1)*ones(1,2);
A=sparse(i,j,s,siz(1),siz(2),numel(s));
A=A+A';

full(A) % View matrix

L=sparse(i,j,1,siz(1),siz(2),numel(s));
logicRelevant=(L+L')>0;
ans =

  Columns 1 through 13

     6     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     2    -1     0     0     0     0     0     0     0     0     0
     0     2     0     0     1    -2     0     0     0     0     0     0     0
     0    -1     0     0     0     0     5     5     0     0     0     0     0
     0     0     1     0     0     0     0     0    -1     0     2     0     0
     0     0    -2     0     0     0     0     0     0     0     0     3    10
     0     0     0     5     0     0     0     0     0     0     0     0    11
     0     0     0     5     0     0     0     0     0     0     0     0   NaN
     0     0     0     0    -1     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     2     0     0     0     0     0     0     0     0
     0     0     0     0     0     3     0     0     0     0     0     0     0
     0     0     0     0     0    10    11   NaN     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0

  Column 14

     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0

Compute maxima allong a certain direction (while omit nan is default)

amaxRows=spmax(A,[],1);
full(amaxRows)

amaxColumns=spmax(A,[],2);
full(amaxColumns)
ans =

  Columns 1 through 13

     6     2     2     5     2    10    11     5    -1     0     2     3    11

  Column 14

     0


ans =

     6
     2
     2
     5
     2
    10
    11
     5
    -1
     0
     2
     3
    11
     0

Including nans

amaxRows=spmax(A,[],1,'includenan');
full(amaxRows)

amaxColumns=spmax(A,[],2,'includenan');
full(amaxColumns)
ans =

  Columns 1 through 13

     6     2     2     5     2    10    11   NaN    -1     0     2     3   NaN

  Column 14

     0


ans =

     6
     2
     2
     5
     2
    10
    11
   NaN
    -1
     0
     2
     3
   NaN
     0

Computing maxima across all desired relevant entries (including "relevant/real zeros")

amaxRows=spmax(A,[],1,'omitnan',logicRelevant);
full(amaxRows)

amaxColumns=spmax(A,[],2,'omitnan',logicRelevant);
full(amaxColumns)
ans =

  Columns 1 through 13

     6     2     2     5     2    10    11     5    -1     0     2     3    11

  Column 14

     0


ans =

     6
     2
     2
     5
     2
    10
    11
     5
    -1
     0
     2
     3
    11
     0

Computin maxima across all desired relevant entries and output NaN where the sparse array only contains "non-relevant or non-real" zeros.

nanOut=1;

amaxRows=spmax(A,[],1,'omitnan',logicRelevant,nanOut);
full(amaxRows)

amaxColumns=spmax(A,[],2,'omitnan',logicRelevant,nanOut);
full(amaxColumns)
ans =

  Columns 1 through 13

     6     2     2     5     2    10    11     5    -1     0     2     3    11

  Column 14

   NaN


ans =

     6
     2
     2
     5
     2
    10
    11
     5
    -1
     0
     2
     3
    11
   NaN

GIBBON www.gibboncode.org

Kevin Mattheus Moerman, [email protected]

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