# [R] Searching a relativ maximum of a matrix

Chris82 rubenbauar at gmx.de
Sun Sep 21 02:48:03 CEST 2008

```Hello R users,

is there a possibility to get the relativ maximum of a matrix?
To get the absolut maximum I use max(matrix)

For example:

The absolut maximum of this matrix is 6[3,6], but the relativ maximum is
6[3,6] and 4[7,6], because both values are the highest value in comparison
to their eight neighbours values.

[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
[1,]    1    1    2    2    2    1    1    2
[2,]    1    2    3    3    3    4    4    3
[3,]    3    3    3    4    4    6    5    4
[4,]    4    4    4    3    3    4    4    3
[5,]    3    4    4    3    3    3    2    2
[6,]    3    3    3    3    3    3    2    2
[7,]    2    2    2    2    2    4    2    1
[8,]    1    1    0    0    0    0    0    0

my first idea was to use this code:

a <- matrix

for (i in 2:7){
for (j in 2:7){
relmax <- a[a[i,j] > a[(i-1),(j-1)], a[(i-1),j], a[(i-1),(j+1)], a[i,(j-1)],
a[i,(j+1)], a[(i+1),(j-1)], a[(i+1),j], a[(i+1),(j-1)]]
}
}

but the code doesn't really work

thanks.

greets
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```

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