# Meaning of : in the parentheses

by jasoncurious
Tags: meaning, parentheses
 P: 8 Hi guys, I am currently doing a Matlab program for partial pivoting. I looked at my friend's example: % Partial Pivoting for i=1:n-1 for j = i+1:n if (a(j,i)) > (a(i,i)) u=a(i,:); a(i,:)=a(j,:); a(j,:)=u; v=b(i,1); b(i,1)=b(j,1); b(j,1)=v; end end end I was wondering what's the meaning of the : in the parentheses. Is it some sort of Matlab keyword? Thanks for helping
 Homework Sci Advisor HW Helper Thanks PF Gold P: 10,196 The colon stands for a whole line in the matrix. Observe: octave:117> m=magic(4) m = 16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1 octave:118> m(2,:) ans = 5 11 10 8 octave:119> m(:,2) ans = 2 11 7 14 ... see? ... so m(2,:) says to take the entire second row while the m(:,2) says take the second column. http://volga.eng.yale.edu/sohrab/mat...colon_operator (Matlab works the same way...)
 P: 8 Thanks bro.
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P: 10,196

## Meaning of : in the parentheses

No worries ;)
Generally, you can try out the confusing operations you see on some random matrix and see what happens ... the magic-square function is very useful for this.

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